He he...
Here's a quote:
"For maximum performance: Look for a pump rated in excess of 300 gph with 1/2” fittings. Match the remaining components accordingly so that true system flow is at least 90 gph. The flow path through the water block should be roughly .06 inches^2 (equivalent to about 0.3” diameter or about 1/4” by 1/4”) to maximize convection. "
The article can be found
here