In racing engines they're pumping a barrel a minute through the engine at high RPM. Higher coolant velocity minimizes hot spots.
I'm using the low mount pump and a 16" 6-blade truck fan, the bottom blades of which extend below the radiator. I had to drop the radiator in the mounting hoop several inches so the fan would clear the lower radiator hose outlet. If I was a good sheetmetal man I'd make a shroud to fit. Instead I added a pusher fan in front of the radiator with a 205 degree-on switch from the Peterbilt dealer and a relay. On a long, hard pull on a hot day it will go over 200 degrees, otherwise runs at 180 per the thermostat.
