Difference between PCI-e 2 x16 and PCI-e 2 x8/x4 is so minimal, that it's not worth worrying about this AT ALL.
Difference between x16 and x1 can be a problem, but not if you do "x16 + x8" or "x16 + x4" combo.
It will be slower, but not so slower that you could actually see a concrete difference.
It usually matters only to FPS-addicts who count every frame, not the absolute majority of mainstream users.
99.99% of mainstream users wouldn't be able to see any difference AT ALL.