Current setup: i7 920 @ stock speed because no matter which way I try to overclock it it throws up bluescreens :/Gigabyte GA-EX58-UD3ROCZ 6gb DDR3-1600XFX Radeon HD 4890Caviar Black 640GBSo anyway, the main question is: how much of an FPS increase should I expect if I were to update my GFX card from the HD4890 to a GTX 480 or 580. I've been testing the PMDG 737NGX out and I have to put autogen settings down to pretty much normal and sparse and lower the texture and mesh resolution quite a bit to get any decent amount of FPS.

Current setup: i7 920 @ stock speed because no matter which way I try to overclock it it throws up bluescreens :/Gigabyte GA-EX58-UD3ROCZ 6gb DDR3-1600XFX Radeon HD 4890Caviar Black 640GB So anyway, the main question is: how much of an FPS increase should I expect if I were to update my GFX card from the HD4890 to a GTX 480 or 580. I've been testing the PMDG 737NGX out and I have to put autogen settings down to pretty much normal and sparse and lower the texture and mesh resolution quite a bit to get any decent amount of FPS.

Graphics card isn't really much help for your FPS. It's really based on your CPU from what I know and what I've read around different forums.

Well, Chris you´re right to a certain degree. FSX is very CPU bound so that a fast GPU won´t boost up that much but If you crank up the AA settings, a faster card will come handy.