I'm interested in upgrading my motherboard for SLI or PhysX GPU. (Yes, in case you're wondering, I will get an EVGA 750w G2 PSU for that. I know.) I was told that the Sabertooth motherboards are highly recommended for performance, but saw some mixed reviews on the Mark 1 and Mark 2 versions on newegg. However, I saw the Mark S version and that is the highest-rated Z97 motherboard. It would fit my case extremely well due to the white PCB, yet is the most expensive. I was also keeping my eye on the ASRock Z97 Extreme 6, which appears to have nice overclocking capabilities as well as a lot of SATA and USB ports. I'm not really interested in an M.2 SSD since using that will take away from available PCI-E lanes for a second GPU. If I were to use an old GTX 660 for PhysX, however, could I force it to run in PCI-E 3.0 x4 mode and reserve the extra 4 lanes for an M.2 drive on the ASRock board? Or should I just get a Sabertooth board?