I'm looking for an amd board that has crossfire and at least supports 1600mhz ram and I notice different boards say they have 2 pci-e x16 slots but have in parenthesis like (1 x16 or dual x8 x8) or 1 x16 and 1 x4. What does this mean and does it make much difference when crossfiring?
This is the number of data transfer lanes available. 16 is better, since it basically means more bandwidth for the GPUs to use, but benchmarks show that 8 lanes is enough for all but the most powerful dual GPU cards, and even those are only marginally bottlenecked (a few frames per second difference at most)
^ But I'd take a step sideways or further. 1x16 is basically a single gpu configuration. dual 8x8 means that if you have a 2nd gpu, the slots will run at 8 lanes each (as opposed to 1 @ 16 lanes) and the 1x4 just means that the 3rd gpu will run at 4 lanes. Be sure that if you want to run crossfire or sli that you'd have at least the specs mentioned above and not just a 1x16 and 1x4.