I'm currently working on a build and I wanted to have a multi-gpu setup using crossfire. My MOBO's details shows the only setup I can have on my only 2 pci-e x16 slots is a x16 and x8. I don't understand, why does my second slot degrade to a x8? Does this mean I have to look for a 3.0 x8 graphics card that fits x16 slot? I'm sure there is a simple answer to my question. Thank you for taking the time.
Here is the MOBO im looking at: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
No you don't have to go looking for a x8 card. Any x16 slot will fit a x16 card but the speed is reduced to x8 in CF mode. This is due to the limited bandwidth on the system bus but it will not greatly impact your performance.
Their's almost no performance degradation going from a 16x slot to a 8x slot.Don't worry about it.
And in real world performance, there's no difference between PCIE 3.0 and PCIE 2.0
Here's a chart shows scaling of Top end graphics cards in several PCIE generations and modes, the only performance hit you get if you connect your card in a X4 rated slot.
And like Purple said and going to say, are you going to use IB? Those chips get hot @ higher overclocks, SB offers the same performance with better cooling.