When you really want to have fun with GPUs, try installing more than one in a Linux system and go for Tri-Fire, aka Triple CrossFireX. Guaranteed fun for months, as you won't succeed -it s**ks bigtime.
Or try combining nVidia and AMD cards in one Linux system and crunching on them both. You might get IT's equivalent of a Nobel-prize! (all in bitcoin of course)
And I can know: I'm trying to install Hybrid CrossFireX/AMD Double Vision on an ASUS F1A75 -that darned mobo without video output-, and I cannot get the APU to crunching!
And I had absolutely no -ahem- problems getting it's more expensive brother, the F1A75-V EVO, into crunching on both APU and GPU!
Multiple GPU crunching on one system is thus at the moment best done by combining an A8-3820 APU with an Asrock A75 Extreme 6 Mobo and three HD 6570s under Windows 7 or 8.
This will give quad CrossFireX without too much hussle and an energy bill that is still payable, as three HD 6570s do not consume that much. Those who can afford place three DDR3 HD 6670s!
Those with money to burn DDR5 HD 66570s or even more expensive cards -but when you have that much money why not buy a
A10-6800K and a motherboard that allows for three video cards?