yes it is backward compatable, and no there be no noticable loss.
so the 3.0 and 2.0 have the same slot?
yes. 3.0 just has more bandwidth, but 2.0 isn't even maxed out unless your running quad xfire/sli
yes, the only difference is pcie 3.0 can handel high band witith which are not currently being used at the moment