82º is a temp that is usually associated with german blue rams. many hobbyists find that 82º is the temp at which they are at their best. plus, german blue rams are often put into discus tanks, where the temps can reach 85º
I would think GBR issues are as with many fish; it's an issue of breeding. You can put a discus from captive bred lines in to a tank with 7.4ph, a bit of nitrates and some hardness, and it'll get by. The same water kills a wild caught heckel. Same thing goes for a gold ram vs. a bolivian ram vs. a wild caught blue ram.
Here's another thought though... more activity means more feeding, higher metabolism, more body load. If I'm not mistaken this will contribute to base pairs breaking down faster. Fish are cold blooded, and tend to live longer in cooler waters that may not be ideal for color or activity. So now we're in to an interesting ethical question of whether it is better to provide a life of neurological stimulation, or a long life.
I think the bottom line for me is that it's all fairly relative considering that we're already imprisoning an animal for our own entertainment, and most people won't be able to make arguments in regards to ichthyoid vs. human neurology or theory of mind. Might as well just keep it at 76 or 82 or what ever keeps your fish alive (i'm assuming that's what most of us want) and looking good or living well; which ever makes you happier.
One thing I noticed: you mention that tiger barbs are tetras. This is not the case. Physiologically they are similar, but scientifically belong to family Cyprinidae. Tetras such as neons, cardinals, black widows etc. are all members of Characidae, a completely unrelated family.