SuAsDu,

I think your going to have to set 14 x 281, if your ram can do 563. I can do 590+, but I have the 8500 SLI ram.
On my Crosshair I found that setting idle cycle limit to 128 in the BIOS and all drive strengths to the min helped get a lot more MHz. You may have to increase the max async. lat. a step or two.
Hope this helps.

Good Luck