Can I mix and match graphics cards?
In order to provide optimal symmetric scaling, SLI Technology requires the NVIDIA GPU to match. For example, a GeForce 7800 GTX must be paired with another GeForce 7800 GTX. Likewise, a GeForce 6600 GT must be paired with another GeForce 6600 GT. However, using the latest Release 80 Graphics Drivers, NVIDIA GPUs sold by different manufacturers can be used together in SLI Mode. For example, a GeForce 7800 GT from vendor ABC can be matched with a GeForce 7800 GT from vendor XYZ.
Can I mix and match graphics cards is one of them is Overclocked by the Manufacturer?
Yes. A GeForce 7800 GTX that is overclocked (for example BFG GeForce 7800 GTX OC) can be mixed with a standard clock GeForce 7800 GTX.