08-14-2013, 07:00 PM
Any worthwhile GPU is going to be two slots wide and require a x16 length slot, throughput doesn't matter just as long as it is the correct length. Looks like the max you could do assuming all of your 4 slots on the back are full height and have one x16 length slot available would be 2 GPUs internally. The AMD 7970 would be a good start or 7990 if you really want to go fast. They do make adapter cables to adapt the correct length of slot if need be as well.