I am choosing trying to choose between 2 9600 gt bfg ndivia cards in sli or 1 8800gtx bfg ndivia for my new quad core system I dont card about power consumption I just want to know if the game play is comparable on 2 9600 gt cards if the frame rate is comparable or if the sli thing is really all it is cracked up to be I thought someone here would have been in a very similar situation and could tell me whats what.
The principle behind sli is very similar to the principle behind multiple cores in a CPU. Personall I would go with dual sli cards (which I assume to be half of the single each, if memory serves).
If you're not sold to nVidia, you might want to look at a 4850. It's only $150, but it'll run most things you throw at it at max or high settings, except something like Crysis. If you want a bit more power, the 4870 is supposed to be good too.
The whole idea of Sli is to take two HIGH END video card and get even more power out of them. (Which in best cases is only a 66% improvement). The best solution is always to get the more powerful single card setup. The Real befit of Sli is main in running in highest resolution 2500+ with most people don't. Check out Toms hardware guide for their very good buying guides for video cards. I'm a big time Nvidia fan boy and never personally will buy a Ati card, but Ati has some very good valued cards out right now such as the 4850 like the post before mine states. If you are really going to get a 8800GTX just get the Nvidia 250 as it is the same card but with 15% more performance and the new tech.
One enthusiast card > Two performance cards. Definitely the 8800 GTX out of those two. However, around that price range, it would be better to get either an ATI Radeon HD4850 (or an HD4870 for a bit more) or an nVidia Geforce GTS 250 (essentially a rebadged 9800GTX+). What resolution are you running?
If you can get rebates on them 2x ATI Radeon 4770 is supposed to be an excellent deal according to tomshardware.com (the review is still on the main page I believe).
Two (or more) Nvidia GPUs are not only for resolutions of 2560+ but also for CUDA and PhysX. As Nvidia made GPUs understand C or C++ they can be used for processing and have been used for physics. Nvidia made the PhysX to utilize physics on a GPU. If you have an Nvidia card your game may not run smoothly with PhysX enabled because mostly they simulate a lot of objects like hail but if you have two GPUs you can have one working on PhysX and the other on graphics. True SLI force.