your problem is that you're using auto for too many settings. and exactly like I said, vcore to auto is not a good idea. I'm assuming that asus programmed auto to rise with fsb, and it doesn't factor in multiplier. That's why you can run 11x320=3520 with such lower temps than 8x400=3200. It sounds about right too. When I set 400fsb, I get 1.6v after performing the vdroop mod, so in your case, 1.5v or so may not be all too off.

Find out what vcore is with 11x320, and you know you can go way higher. Your end goal should be 9x400 or better.

http://www.wittekakker.be/projects/p5b/index.html