if your 56th can work stable with 930+MHz - you have to keep 56th bios =) If not - 64th bios will allow you achieve 1100MHz stable and get more hashes. ( 56th @ 930 ~ 56th -> 64th @ 1100 with CN algos)

As for me - i've noticed that mem speed for V8 gives poor hashrate growth, so my Vegas are at 1070MHz and wattage difference i'm using with core speed =)