Say that I get an XFX 7900GS soon. Then, later on when new stuff comes out and prices drop, I decide to get another 7900GS. But - what if, for example, there are no more XFX 7900GS's to be found, but there are EVGA's? Would I be able to get that and then SLI the two, even though they are from diff. manufacturers? Also, what about models? If I get a model-A 7900GS and then a model-B 7900GS from the same manufacturer, will it work (XFX has like a thousand 7900GS's, no idea why....)? And, if they are diff. companies AND with different clocks (for example, XFX's normal 450mhz and EVGA's F-OCed 500Mhz)? Thanks in advance!