Hey guys. Just letting everyone know that might be interested.
I own both a Ati Radeon 4850 512, and a Nvidia GTS 250 512.
These are equivalent cards with the same amount of memory.
I have been using the Nvidia since I bought it (had the 4850 first) and found the results to be much better with the Nvidia card at the time. I have had it for about a year.
I just switched the card out and put in the 4850 to see how it would compare. So far I'm very pleased. It seems to be about on part with the Nvidia card with playing games. But the biggest difference I have seen has been with firefox and flash... I'm very surprised by this because I wasn't expecting any difference. I have noticed that flash has not been performing very well with FF 4 so far, but when I put in my ATI card it was like night and day. I have a feeling that something in the internal workings with FF has taken out the video acceleration from the Nvidia card and ATI still has the acceleration function.
Nvidia still seems to work slightly better with Kwin, but it's negligible. I haven't tested any movies or videos with any players yet (mplayer, vlc, etc)
I would very much love to post some actual frames per second results with the phoronix test suite or something, but I haven't been able to get it to properly work on Pardus yet. Would be nice if we could get the GUI working for it...
Edit: Oh yeah, my flash results were mostly taken from the flash games using facebook. Most notably Age of Champions. If you don't play that, you should it's rather entertaining