I want a rig where i can run beefy settings for Dishonored, Borderlands 2 and BioShock: Infinite.. and i was unsure whether the 5850 could pull that off.. but it appears it won't do me any better to "upgrade" to a 7750.. meh..
If you're not happy with your current framerates, maybe you should think about getting a better GPU. Both the HD7950 and the HD7870 are good options. If you want something more beefy you could look into a GTX670, but it's priced at U$399.
The GTX660Ti is also a great option. It's much better than your current GPU and isn't too expensive. All these cards i have mentioned support DX11.1, while the HD5850 doesn't.
I will probably upgrade my GFX card before this time next year, but i actually don't think that the 5850 is the cause of my poor performance in games..
It's pretty much most newer games atm that are giving me trouble, Skyrim is choppy as hell, and even some old stuff like Gothic 4 is runnig badly.
the 5850 is the newest addition to the system.. bought in March 2011.. while ALL the other parts are from June 2008.. so i suspect it's one of the really old parts that causing the problems..
But as i said.. come christmas or maybe after new years, i'm probably upgrading the GPU too, i just don't think it's an immediate issue :) (if it turns out it was the GPU when i get the new system, then i'll of course upgrade :P)