I'd try overclocking your CPU as well... Reviewers all over the internet manage to get quite high FSB's with that mainboard, so you could try it as well...
NeoSeeker: 280MHz
PCStats: 262MHz
The Tech Report: 260MHz
NinjaLane: 245MHz
Viperlair: 240MHz (They use a processor that's hard to overclock...)
HotHardware: 230MHz? (Man, their method sucks... Leaving the multiplier at 11x...)
If you do it the same way as NeoSeeker, with a divider because that RAM of you won't be hitting high..., you must be able to overclock your CPU to a FSB of 245MHz, hence a 3500+, or even more... I know it's a Winnie, but some of those chips also managed to hit 2.6GHz, so it should probably even work trying to get to 266MHz, then you'd have an Athlon 64 3800+...
Although overclocking doesn't gain you a lot on that 6600GT, go for it as well, some extra frames are always welcome... Use
CoolBits to overclock it...
Good luck...