PCI-SIG announced the availability of the PCI Express Base 2.0 specification on 15 January 2007
. PCIe 2.0 doubles the bus standard's bandwidth from 0.25 Gbyte/s to 0.5 Gbyte/s, meaning a x32 connector can transfer data at up to 16 Gbyte/s in each direction.
PCIe 2.0 is backward and forward compatible with PCIe v1.x. Graphic cards and motherboards designed for v2.0 will be able to work with v1.1 and v1.0, and vice versa. In some rare cases it is possible that a PCI-E 2.0 card will not work correctly on a PCI-E 1.0a slot. This is only limited to certain video cards.
The card will not perform at its max and you will loose some frame rates but it shouldn't be to noticeable. Besides depending on your system the graphics card interface won't be the only bottleneck.