The heat is gone, that was the main reason for removing the cats on my Viper. After a 30min drive the heat inside was unbearable, with the cats gone I can drive as long as I like and keep the AC off.
The power gain is there but so is the noise. The car gets much, much louder and unless you are willing to put up with the sound consider other options. Personally, the car sounds as it looks now which is a good thing.