I'd get the GTX personally.. I run 2 9800gtx+ in SLI right now and there great cards for a good price. I'm not much of ATI person so i haven't really tryed or used that card.
It really does depend. First off, WHICH GTX2 are you getting!? A GTX295 will wipe the floor, where as even the GTX275 will destroy a HD5770. A GTX260 is on par with both the 5770 and 4870 which are both of almost equal ground. The 5770 though, being more new, may get better driver support in the future, and supports DX11 and tesselation. DX11 will probably run better than 10. I may doubt that the card though fine now, will have the firepower to run tesselation. Get 2 however, and you will have the power to last sometime. Get a 5850 =D
nVidia, you have CUDA, and all the general processing through C, and stuff... PhysX? interested? No? lol...
_______________
********* EDIT: I just read that you have a 8800GTS 512. What is the point of getting a 9800GTX+ if you are alrdy have a 8800GTS 512. All you get is the same f'king card with the same core but a different stepping, thus higher clocks. Seriously, unless you are getting a bombing card, no point of upgrade. Damn dude, many of us are still running cards with multiple pipelines! - Pre - DX10 cards! You are wasting your money! Save the money, and/or sell the card, and boast to everyone with a 5870! You can probably sell that card for $120 (70 Euros?) ********* --- upgrading to a 5770 may only yield 10 % more performance... Overclock those original G92s that I envy. All these new rebranded G92s are pissing me off, though I still love the original 8800GT / GTS =D
For me however, upgrading to even a 5750 will give me like 4x the performance! 7600GT sucks ass ~~~ though it runs LFS @ 1080p all high no hiccups =D
