Youve probably hit the FSB wall here. Its either your chip or your mobo. Try feeding the processor a bit more vcore and check. If it overclocks beyond 2.9, it was your CPU. But if it doesnt OC beyond 2.9 despite increasing vcore, its your mobo thats limiting you.
It could also be your PSU since these Xtreme power PSUs arent the most efficient of supplies. however I doubt that it is, because the PC wouldve probably refused to startup had it not been getting enough juice.