4 x 1 are most of the times cheaper then 2 x 2, and the 2gig dimms aren't that overclockable...

With ya P5W and a quad it will be around 3 - 3.2ghz, P35 or even X38 will give ya much more FSB freedom... but do those 300mhz or 400mhz will make a difference ? I would settle with 9 x 333Fsb you already got nice quad OC there (QX6850 level)