I haven't tried two pumps, but thinking about it I wouldn't. The two pumps would have to somehow be set to have identical flow rates or you would have turbulence created within the cooling system from slightly different speeds. Since a vast majority of the pumps being sold are set to one speed only, the chance to even out the flow rates wouldn't exist. Besides, seeing as you have decided on the MCP650, the 317GPH flow rate should be more than enough to handle the processor, VGA, chipset and even a goodly amount of overclocking to boot.