ATI Radeon 4850 and Nvidia GTX260 SLI?

You can't combine an Nvidia card with an ATI card. 2 different companies, 2 different architectures, 2 different pieces of hardware.

I'm not sure about the 7900gt, although i'm pretty sure it doesn't support sli. Anyways, thats a mute point since it would terribly reduce performance even if it could.

When you crossfire/sli two different levels of cards, say an ATI Radeon HD 5770 and a 5750, the 5770 has to be scaled down to the performance level of the 5750 to work.

With Nvidia the cards must be same. The 7900 IIRC doesn't support Phsyx so you couldn't use it for that either.

Ah, ok. yea, i'm pretty sure ati's cards can crossfire within the same level of a series, eg. 5700s can crossfire but not a 5700 with a 5800.

Ok thanks. How much better would two GTX 260s compare to just one?

Is that a question.! Two cards will obviously perform better than a single card.. The power draw will be higher though so you need to ensure your PSU is capable enough to handle it..

Just go for a whole new card instead of SLi or just use a single GTX 260 since its getting obsolete.

Obsolete? lol, wowww

Is, not "getting".

S'true.

If by obsolete its meant hard to find for a retail purchase then that may be the case.. Performance wise, its still a capable card and It'll be more of a wiser decision to stay put and wait for the next iteration of video cards to launch.. As per few reports floating on the net, ATI may be out with the 6XXX series by as early as october..

i doubt we shall see the 6xxx series from ati in October, and besides that's a pretty long ways off.
If your interested in a new graphics card though, the 460 has gotten good reviews