I would say it's average. When you say FPS, what games do you play most?
Games like CoD4, the Source games (Portal, TF2, Left4Dead) would play ok on a 8600 GT
Crysis and Far Cry 2 is definitely a little out of league for that GPU.
I once saw an ASUS on Newegg with similar specs, but equipped with a better, faster 9600 GT.
Price was around $1300: a good bargain. But I've lost that bookmark.