While Intel official site does state that the version of Pcie slot is 2.0 (I guess 2.x means 2.0 right?)
Some other sites and the box that my motherboard came in state just it has Pcie x16 slot and does not specify which version.
Like another source from intel: http://downloadmirror.intel.com/17250/eng/DG41RQ_TechPr...
I searched around the web alot looking for an answer and came across a software that could identify the Pcie details and many other details of the system in a much detailed manner.
I dont know if you guys know about PC Wizard 2012 (Created by the same makers of popular CPUz)
Even the software stats I have Pcie 2.0 x16. (I want to post a picture of those details but dont know how to do it hear)
Pci express 3 is fully backwards compatible with pci express 2, you simply wont get the added speed benefit but it should work just fine, no worries.
There are rare occurrences where the on-board video is not automatically switched off when a discrete card is put in. If you put in your card and don't get a display from it, check the on-board and see if there is display, if so you need to disable on-board first. You should not have to worry about this though as almost all boards flawlessly switch over when a discrete card is detected. If you do run into this issue just google disable on-board video, its simply a quick setting in the bios.