i cant overclock my q8200, when i increase the FSB even by 1 the whole system locks up and i need to reset my bios.
What's ur chipset and mobo?
As for the question you should get a HD 5850, don't waste your money on a 5970 except if you have a monster of a monitor or wanna run eyefinity
That cpu won't be much of a bottleneck for 5850 even @ stock unless you're gaming on a extra low res (800x600, 1024x768)
Oh, you said you wanna upgrade to core 2 extreme. DON'T waste your money on it! LGA775 is a dead socket for upgrade. You'll be way off better buying Core i5/P55 platform;)