i'm setting up a water cooling system and i am having trouble finding the right pump.. here are the parts:

Polarflo sf cpu water block
polarflo vga and chipset water block
1/2" tubing
duel 120mm radiator

the polarflo cpu block says i at least need 300 gph.. is 500 over kill?..and the chipset and vga are going to use duel tubing..is that ok?