It'll work FINE.
There will be as close to ZERO performance difference as you can measure
between PCIE1.0 and PCIE2.0, don't worry.
I'm sure if you had a video card in an x4 slot then you might see a difference
between the two, but at x8 or x16 you're NOT even coming CLOSE to using all
the bandwidth of even PCIE1.0.
Sure some things would be slightly sped up, but it'd be irrelevant to real world type
games and video cards. The games are all DESIGNED around people having
PCIE1.0 slots, and X8 instead of X16 at that, so they definitely don't NEED
PCIE2.0 x16 to work at full potential.