Let be honest, I don't know what are you talk about GTA IV doesn't support SLI cards.. You hold old fashion way like 2000 or somethings.. You had no experince with SLI/ TRi card or whatever. I did play High ended game GTA IV on SLI cards, I was like the WOW factor. it runs very friggin smooth motions and high fps rate without lag.
I really thank to overclock.net about sli cards and build pc. Fourms has tons of infomations, tips, etc.. they are awesome feedback and encourage.. they are the hardcore fan of SLI, TRI, QUAD, Multi CARDS like me.
when I joined Nvidia SLI site, I learned a lot from sli, tri users's comments on forums for 10 months.
Link 1 and
link 2
8000 & 9000 series are the true dedicated PhysX as multi card which can runs with any high ended single card or sli cards.
So, I won't forget what you said "gpu wont runs with different gpuif 2xsli". I will find your post somewhere this forumns.
any GTS250 is capable with 9800GTX+ for SLI-
Link which is evidence enough!
Lokk at picture below from OC.NET-
ATI Radeon card can with Nvidia card as dedicated PhysX, but dont require sli configuation.