You're right as far as performance go, but I chose the MCP655 for a reason; It's known for it's excellent reliability, while the MCP3xx pumps have a much higher amount of failurs. I wouldn't care for it, but since I do not live in the states and I'm doing an international order, RMAing something...
In martinsliquidlab.com you can see that the FuZion V2 and the GTZ performed the same on Q6600 (without quad core nozzle/insert).
And from EK Supreme tests the difference in temps is so small (0.x c as far as I recall) and IMHO doesn't justify a (roughly) 0.5gpm flow rate decline, plus it's...
Going to cool a quad core + 4870. I thought about something like this..
CPU block: D-TEK FuZion V2 - same+- performance as the GTZ but less restrictive..
GPU block: Swiftech MCW60 Rev2 or D-TEK FuZion GFX2 (too bad no one knows anything about the MCW60 rev2 yet)
Pump: Swiftech MCP655...