Shame on you!
I'm not convince you would notice any difference upgrading from an already good cpu (Dual Core 2400MHz/4MB Cache/1066MHz System Bus).
Doom 3 benchmark [timedemo demo1 usecache]
1600x1200/Ultra/2xAA/V-Sync Off
X1950XT 512MB
E2140 @ 1600MHz = 78.6 FPS
E2140 @ 3200MHz = 93.0 FPS
E6300 @ 1866MHz = 81.7 FPS
3000+ @ 1800MHz = 67.8 FPS
3000+ @ 2400MHz = 80.0 FPS
an extra 1600MHz and I get 14.4 FPS gain?
Not sure if its something to do with the GPU hitting its max or just the way the game is coded?
What kinda games do you play? are they FPS or RTS?
If its FPS then as suggested a more powerful GPU would get you some serious 'action' but if you favour RTS then perhaps a faster CPU would be the better option. . .