Whilst higher temps. increase activity and therefore appetite, it has been bought to my attention that this could significantly cut short a fishes lifespan.
Having observed the behaviour of a sub-adult female Convict at either end of the scale, i found that the fish became rather aggitated and/or distressed at temps. greater than 28*C (82*F?). And seemed to have aquired a skin irritation (parasite?), which would prevoke intense scaping of the flanks, eye's and behind the gill plate. I read also they will become more suseptable to disease in such condition's.
At temps. below 22*C the fish appeared lethargic, consuming less and therefore would lose condition. Again, easily prone to disease.
My conclusion was to keep a temp. of between 24-28*C. Personally i try to keep my temps. hovering around 26*C during the warmer period of year (it has peaked at 32*C with a 40 odd *C day). And 24*C over the cooler period.
If you were willing to take on any info. from my deranged little study, i'm happy to have helped.