Geil's ddr533 could do 540, but that's it, if you get OCZ PC4000 copper series they could do 550 at lower cost and lower voltage.
-Intel PIV 2.4C @ 3.84G -Asus P4P800 -OCZ Copper 2x256 4000EL memory @ 275mhz 3-4-4-8 -Sapphire 9800pro @ 490/780 -SB audigy -80G Maxtor Diamond Plus9 Ultra ATA-133 hdd -450 Enermax PSU