I run my controller at 83.5F and mix NSW at 1.026-1.027, bit different than most it looks.

Wow, really ???
That's a whole lotta up there ....

I'm running 80f and think it's my limit

My SG is 1.025 for now, both DT and QT

I follow Ron's logic in the link above with regards to sea life metabolism being a large part of their immune system and metabolism being directly linked to temperature. I just try to match the average reef, IMO lower salinity and temps have been a LFS cost saving technique more than any science.

Do you have any temperate species in your tank (margarita snails, etc.)? If so, how are they holding up?

Nothing special species wise and everything seems happy and active. My post should read 82.5 instead of 83.5, typo, with a .2 swing either way on the Apex.

I hate border collies, always jumping on my head at 4am...anyway, since I was up, I read a few articles on temp and based on these, similar to the link above, I'm going to raise my temp to 79 or 80 to see what differences I can notice. I guess I need to buy a heater :)

For sure... extra investment that you will have to get when up switch over to LED.

When I had my 150X2 MH and 54X4 T5 over the 75gal before, heater never turns on, but chiller does even in the winter time.

However when I switch over to LED, heater actually turns on first time in 2 years.

For me, I have the heater kicks in at 75 and turns off at 76. and with 1 degree drop at night.

From all my 4am reading, that's too cold for corals. That's where my tank has always been, but I'm going to raise it and see what the corals do..

I set the summer time temp lower because tank is now on a different floor, and with all LED. I am not too sure how will the temp rise up during the summer. So I set it lower, that way, if it shouldn't rise up to an alarming level. Even when it does, I should be home already and deal with it.

I've been running my tanks @ 80 due to Ron S info
I am starting to trust in the thoughts of the higher temps .....
Not just based on fishes but the metabolism of corals