you are correct that electrics work well at near idle conditions, but you must remember that it is not a matter of engine rpm as the fan is overdriven by the pulley ratio to work in the rpm required by these motors.
Originally posted by FASTERTHANU
I made a quick call to flexalite tech dept and he (name removed to protect the innocent) said as a round number the turbo diesel clutch fans move about 12,000 cfm (that's 12K) when locked up at 2000 rpm and they (flexalite) do not recommend electrics as primary cooling for these vehicles, but rather as supplemental to the existing system.