Yeah, don't get too worked up with flow rates. If it's one thing I'm really learning about thermal performance is that flow rates above 1 GPM really don't make all that much difference. You really have to start getting down into the .7 GPM range before the thermal curves for blocks and radiators start dropping off.

So I agree with Tommithy's response. It doesn't matter if it gives you better temps. The other interesting thing about pumps...they dump LESS heat as you add restriction. It's the increased RPM in the pump motors that increases a pumps power consumption at any given voltage. I would have thought added resistance makes a pump work harder and dump more heat, but it's the other way around. It's the motor spinning too fast and acting as a brake.

Anyhow, in a CPU only loop with the latest high surface area blocks, flow rate becomes less and less important. 5 years ago when everyone was running low head pond pumps and large channel type blocks, flow rate was much more critical. Partly because the pumps didn't have the pressure capabilities without alot more heat and also because the thermal curves for those older blocks dropped off much more rapidly. Now with all the micropin/nozzle block you still get very turbulent flow and good mixing at lower flow rates.

My 2C.

I'm thinking the 5.5mm nozzle for dual cores and the quad nozzle for quads is a good place to start with standard pumps.