Hard to say what each individual should be looking at with any particular LED solution, since we all have slightly different tanks & requirements with respect to the livestock we choose to keep. If someone is having success with a particular size tank that's similar to yours, especially with a PAR38 set up, you will likely be in the ballpark for your own system. The great thing about the PAR38 form factor, is you can always add another without too much rewiring. PAR38s are continuing to evolve with more and higher power emitters being installed in them all the time. Pretty sure I've seen some with 12 individual LEDs in them.
I was at the Home Depot yesterday and there are already a number of new offerings in the LED lighting section compared to when I was last there a few weeks ago. The lights Steve (StirCrazy) purchased for home lighting are currently on sale for under $13, so I picked up a couple more myself. This price would have been unheard of just a few months ago, let alone even having something of this nature on the shelf. Not for aquarium, but the writing certainly appears to be on the wall. Other lighting technologies will eventually be eclipsed by LEDs.
I mentioned I was looking at a 12 volt DC solution with my MR16 schtick. I just read that one of the LED manufacturers is actually working on an AC powered LED, no driver required. Most folks may not be aware of the fact that conversion of AC to DC to run LEDs (DC devices) results in a 15 to 30% power loss in the process. So each of those Meanwells, buck pucks or whatever driver you use, is consuming extra power that would be better utilized using a straight DC voltage source.
I just ordered a couple of these to see how they may work:
They are 10 watt Cool White LEDS & the price is right for experimenting. Chips similar to these although at 50 & 100 watts look to be the ones used in the Ecoxotic Cannon type LED lights that cost a freakin' fortune. By buying these chips yourself, with the reflector & lens assemblies, you can build something similar for less than $50. I got two sets of two of these for $21. The reason I chose the 10 watt jobs is again, they can run directly off 12 volts DC. Might be wise to add a regulator/driver to ensure the voltage & current does not deviate too far off the 12 volt nominal voltage. If this ends up working well, I may ditch the MR16 build and do this instead, or a combo. To me, the craze in DIY LEDs seems to be single Cree emitters in the 3 watt range. Not sure everyone needs that much light and am trying to see if alternatives such as this are viable.