These Asrock boards are a stepping stone solution towards a full blown c2d - pci-e - ddr2 system. The best clocks are achieved with an agp gfx card and ddr1 ram.
They will generally reach 300fsb but add in a pci-e gfx and you'll need to clock it back a bit to remain stable. Add in ddr2 ram and you'll stifle it even more, probably be stuck around 285fsb, so ddr2 is fine if you intend to quickly move onto a new Gigabyte, Asus etc mobo but I don't recommend ddr2 as a long term upgrade with the Asrock.