COLGeek :
Yes, the PCIe 3.0 devices are backwards compatible with earlier PCIe standards. Not a problem.
AMD (current) PCI-E 3.0 cards are NOT
generally backwards compatible to PCI-E
1.1 and earlier, but Nvidia PCI-E 3.0 cards
usually are. See this issue discussed here:
http://www.overclock.net/a/the-final-answer-to-the-controversial-pcie-x16-version-compatibility
I'm aware the OP has PCi-E 2.0 slots, so this doesn't apply, but just to clarify on the general compatibility status of PCi-E 3.0 on earlier gen PCi-E slots.