I read the previous post you are talking about and I didn't see anything that you haven't said in this thread, so I agree we don't need to revisit it.
Everyone uses different terminology. I consider internal skimmers ones within the aquarium, which fell out of fashion 10 years ago. External skimmer is assumed, so I haven't heard the term in a long time. I locate external protein skimmers in sums to catch drips, overflows, and act as a fail-safe.
A 10x flow rate through the sump to be an industry standard or common knowledge. I did a search on Wet Web Media and the first article that came up was this one which recommends a 3-5x throughput.
http://www.wetwebmedia.com/circrat.htm
I'm not arguing that a 10x throughput won't work, only that it is inefficient and a poor use of resources. An 800 GPH pump is suitable for a 200 gallon tank as a sump return. I don't agree that it would be a good choice for a 20 gallon tank.
Protein skimmers are limited to removing a maximum of 25% of the TOC so there will always be a buildup of dissolved organics that the protein skimmer cannot process. Your example of the two skimmers doesn't apply to our discussion of how much water to move through the sump. If you believe Escobal's theory that the proteins need a two minute dwell time for optimum bombardment time, then the skimmer with a more concentrated feed and longer dwell time will be more efficient than the second example you offered where less concentrated water is processed quicker. The two schools of thought are filter the water slowly and thoroughly, or quickly and less thoroughly. I agree there is an argument for either method, but the subject at hand is "do you move more water through a sump than the amount the protein skimmer will process?".
The secondary question is do you use a sump design that guarantees the skimmer processes the water only once before returning it to the display tank, or do you allow the skimmer to process the water numerous times while new unprocessed water bypasses it?
A higher volume turnover (10x) will cause the water passing over the overflow to crest higher. You will have around 1/2" of water skimmed from the surface. With half of that flow (5x) you will have 1/4" skimmed from the surface. The extra 1/4" collected with a larger pump will not move the surface water any faster, it will only dilute the surface film collected. Allowing half of that diluted water to bypass the protein skimmer due to an oversized return pump, coupled with a sump design that allows the water to be reprocessed over and over makes the system even less effective.
A horizontal barrier for an overflow is a piece of horizontal acrylic, eggcrate or glass that sits above the overflow edge perpendicular to it. It acts like a long slot rather than a series of small slots. It stops fish and inverts from getting through the same as vertical slots. Nothing gets trapped in the dry part of the overflow. The other way of draining without losing half of your surface area and breaking surface tension with teeth is to have a smooth overflow edge and place gutter guard mesh just inside the overflow box. As there isn't a gap, nothing will get stuck in the overflow and dry out.
There is no head loss with a closed loop even if you locate the pump in a basement because the intake is at the same height as the return. There is some friction loss if you use too many elbows, but Tigerflex hose minimizes it. Powerheads are a poor choice for added flow because they do not have adequately diffused intakes so they can injure livestock. They also cause heat transfer, vibrations, stray current, and poor flow dynamics. An external pump closed loop has a higher upfront cost but lower operational cost and more longevity (10-20 year pump life vs. 4-6 year pump life). The popularity of powerheads stems from low $50 increments needed to implement them. If you are on a budget, they get the job done without major drawbacks, but in the long run the cost more, require more maintenance and are less efficient.
Your current return pump RE65m3 (1717 GPH @ 65 watts) moves approximately 10x the volume of your display tank. If it was replaced with an RE25m3 (660 GPH @ 38 watts) it matches your skimmer pump which I estimate to be about 500GPH, and you would save 27 watts. Prop powerheads are not accurately rated for water movement so the flow rates the manufacturers offer, but let's assume they are accurate for the sake of discussion. You claim you are getting 3000 GPH @ 45 watts from the two powerheads combined. Using your numbers, you could add another powerhead for 22.5 watts and add 1500 GPH flow to make up for the 500 GPH you are dropping by matching the sump turnover rate with the protein skimmer intake. You would have a net gain of 1000 GPH flow with no bypass of the protein skimmer. There are numerous benefits for draining less water mentioned already.
A closed loop system offers the following benefits if executed properly...
1) Hidden influent and effluent lines.
2) Less heat transfer.
3) Less chance of stray electrical charge or shock hazard.
4) Less vibration.
5) No electrical cords in the water or running over the top of the tank.
6) Easy access to intake strainers.
7) More laminar and less turbulent flow for better inertia.
8) The ability to position flow anywhere in the tank.
9) Easy removal of pump if necessary.
10) True flow volume ratings.
11) High pressure flow.
12) Long pump life.
13) Only one cord to plug in.
14) Better circular flow.
15) The ability to locate the pump in a remote location (service area).
I make my technology and methodology decisions based on a thorough thought process, not based on my 30 years of experience in the hobby or 22 years experience in the aquarium industry
In the 70's & 80's we used a 3x total flow rate for the display tank. In the 90's, a 10x flow rate became commonplace (likely the source of your information), and in recent years 20-40x has become the acceptable range. From my experience quality is better than quantity. If you use powerheads randomly aimed at the rock formation or front glass, you will need 40x flow to get the results you are looking for. If proper flow dynamics are implemented (circular flow, laminar flow, and up-flow for suspension) then you can get by with as low as 15x the volume of the tank for total flow.
The Herby method of draining was common in the 90's. It fell out of fashion after the Stockman and Durso modifications were introduced ten years ago. The problem with the Herbie method is it allows for a small drain point (one you can't even monitor) that can potentially clog. A safer system is a true siphon drain with a Stockman or Durso emergency drain.
I don't think you can fake a car in a car show or a tank in a TOTM. My point was a TOTM is a chance for everyone to see a nice tank that is successful, not a chance to follow the owners learning curve. You will see every possible method with good results. As a result, it's hard to measure their success and decide on the merits of the system. TOTM owners aren't required to explain or defend their methods. It's just raw data with a few anecdotes. I read a lot of books and articles and spend a lot of time on forms. I just don't have time to read a TOTM write up. I skimmed your tank build thread, but I would have read it if I was on this site as it played out. I guess news is more interesting than history to me
Europeans don't use T5 because it's better, but because it's cheaper. I lived in Europe for the last year and I can tell you from talking to hobbyists and industry people, MHL is preferred. T5 picked up some interest a few years ago, but they are waning in popularity now. Hydro rates are much higher in Europe, as is fuel. They all drive diesel over there (which I prefer) but they wish they could afford our gas guzzlers.
My clients look for aesthetics (or fluff as you call it), not fancy equipment or rare livestock. There is no point in putting filtration details on my website. I have lots of pictures posted on other forums (RC etc.). I prefer to modify cost effective filtration devices and lighting, rather than throwing money at overpriced equipment and haphazard configuration of it. I don't do maintenance or much in the way of stocking so I don't have many pictures of mature tanks.