You don't need PCI 3.0, any 3.0 card will work in any 2.0/2.1 slot. Like I said I almost bought one, but decided to stick with Gigabyte because that's what I've always used and the BIO's are the same I've always used.
Actually I didn't even notice at first but the ASUS board is only AM3 socket. Since it comes with an AM3 CPU it doesn't matter, unless, you want to upgrade at some point. Then you will need a new board.