By the way, currently I have 4670 GPU, run PCI-E 1.1 x16 (32MH/s with 750MHz > 800MHz clock using cgminer).
So, if I move GPU to motherboard that capable PCI-E 2.0 x16, dose Hash rate will increase? i think not
I was getting 35Mhs on my AGP 4670. So I would expect you should be getting higher than that already.
But no changing the slot/MB won't help.