yes PCI 3.0 and PCI 2.0 are fully compatible: PCI Express 3.0
PCI Express 3.0 Base specification revision 3.0 was made available in November 2010, after multiple delays. In August 2007, PCI-SIG announced that PCI Express 3.0 would carry a bit rate of 8 gigatransfers per second (GT/s), and that it would be backward compatible with existing PCIe implementations.
Thanks for this answer was pretty sure it was backwards but started doubting my self, is it also true there is currently no real reason to jump to a 3.0 mobo and it is a marketing ploy?
i don't think of it as a marketing ploy, there are some insane quad SLI set ups that do benefit from the overhead bandwidth. but for the most part PCI 3.0 isn't necessary for excellent performance for most users.
This year , a 3.0 mobo isn't needed and I'm doubtful it will be next year. I bought a z77 instead of a z68 to help future proof.
You should say most people don't need PICE 3.0. Some with PCIE based SSD's make full use of the bandwidth today. Those who run 3 or 4 graphics cards in SLI / Crossfire could use the extra bandwidth.
To pile on what others commented, you will be just fine running the card in a PCIE 2.0 slot and you will see no performance degradation. Click buy, happy gaming.