Depends, if you EVER plan on using a 2nd GPU -- IF yes then the Z68 Extreme3 Gen3.
Assuming the following (2):
Z68 Pro3 - http://www.asrock.com/mb/overview.asp?Model=Z68%20Pro3
Z68 Extreme3 Gen3 - http://www.asrock.com/mb/overview.asp?Model=Z68%20Extreme3%20Gen3
I am not an advocate 'today' with PCIe 3.0 just for the GPU(s). If you're only going to use (1) GPU it will run PCIe 2.x with the Sandy Bridge, OR PCIe 3.0 IF you replace
BOTH the CPU for an Ivy Bridge AND GPU(s) -- with or without the 'GEN3' 'Switching Chip' = for 2 or more GPUs. The NEW GPU must be PCIe 3.0 -- none of them are out and even the fastest Gaming GPU barely saturates the PCIe 2.0 x8 lanes and none are close to PCIe 2.0 x16 and it's laughable for PCIe 3.0 x16 -- maybe in 5 to 10 years.
Meaning 'GEN3' for GPU only is Snake Oil.