For pumping up small fry, I keep the temp around 82-86. Once the fish are large enough to display as masterpieces, I suggest you slowly drop the temperature to the minimum temp possible ~72 to maintain show quality colors and kok. This is because you can greatly extend the life of your fish by lowering the temp and feeding less.
There was a study a while back that studied longevity in Betta Splendins. The typical Betta live around 2-3 years in the average home. Researches fed their fish a minimum amount of food and chased the fish around the tank daily for exercise and their fish lived 7+ years.
Simon