I cannot vouch for the Asrock board, but from personal experience I would absolutely recommend the Asus Maximus IV Extreme-Z (which I recently replaced for Maximus IV Gene Z for my HTPC due to size constrains) I've heard good things about Asrocks latest boards, but IMHO, Asus is the best board manufacturer ATM.
About Gen 3, well there's currently no video cards that use the spec, that'll change pretty soon with the release of AMD's 7000 series and Nvidia's Kepler, but to be honest with you, there's no cards that saturate PCI-E 2.0 yet, and I doubt these new cards will even utilize the full bandwidth available to 2.0 spec boards.