Will give you 3-5% perf increase. It is optimize memory access... You can enable it in bios. Sometimes memory wont take it if its already close to the edge but it should be ok!
Asus P4P800DX, P4C 2.6ghz@3.25ghz, 2X512 OCZ PC4000 3-4-4-8, MSI 6800Ultra stock, 2X30gig Raid0