purple stank said:
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.