What application do you have that you think 4 graphics cards is a realistic expansion path?
Adding additional weaker cards gives diminishing returns if you are thinking crossfire/SLI and gaming.
If you are looking at running 8+ monitors <4 cards might make sense> then what applications are you doing that with, how many monitors and what resolutions?
The crosshair is an "AM3" motherboard, which means it is for AMD CPUs, not intel.
For the best SLI motherboards I would go with EVGA instead of ASUS, if the price isnt much different.