Wonder if there will be better performance by setting the 9800 GTX as PhysX with my other card GTX 570. Is not in SLI. (heard that it was not necessary.?)
For now the PCIe x16 connector to the GTX 570 just go on x8, it may be that the GTX 570 give better performance when it runs alone on x16?
And if I gonna buy a second 570 for SLI, does it need to be exactly the same card, manufacturer etc? The one I have today is Asus GeForce GTX 570 DCII 1280 MB
What should I watch out for?
What about cooling?, they will stay very close.
Is there any O.C options/possibilities, for this card? with or without SLI?
And my PSU is Corsair TX750M will that be good enough for SLI?
I see no problems with your PSU for SLI. It doesn't matter if the cards are from a different manufacturer or model. Using the 9800GTX for PhysX won't have much of an impact so I'd say your better without.