It all depends how it comes setup.  Bear in mind my system isnt much different than yours bar I only have a 3500+ cpu.

With everything set at standard stuff in BIOS I scored 21700 in 3dMark01.  After a few little tweeks here and there I now score 23978.  Im still twiddling though and reckon I can pip the 24000 mark!

Anyhow from tweekin my system I have gained over 2000 points which is a fair gain and a noticeable one.  I watch the tests each time and the FPS gain was very noticable in the tests.

Remeber though tweekin stuff can go wrong sometimes, i was playing earlier tryin to get more outta my CPU (Which I am strugglin with at the moment) and it all went tits up!! had to clear CMOS etc and start afresh, not to big a deal though as I always write down my tweeks so i can revert back and start again!