Maybe I'm not so tuned in to minor video effects, but my last three video card upgrades )over several years) seemed to produce very minimal visible changes. The cards all were fine, and my 5850 seems to run Crysis 2 fine at 1900 on my 24" monitors. Grading audio to Xonar was dramatically different.
I'm thinking of upgrading to a 670 - but wonder if once again the changes will be so minor I'll wonder why I spent the $400 bucks. Yes, the shadows may have some greater detail, the reflections be a touch more complex - but I usually am not staring at them while avoiding getting my butt kicked and offing aliens.
I see some "huge improvement" lines in reviews by upgraders - but what's likely to be evident? The 5850 has been remarkably competent.
System is P8P67 Pro, 2600K, Corsair 520 PSU, 8 gigs mem, Xonar, 256 M4 SSD, etc.