probably the reason the nissan 350 uses a clutch fan is partially the grill sizing and speeds expected. As DKjones said, once you are driving faster than the electric fans spin (or even close) they become a restriction on or off. e-fans are most beneficial for both economy and power in city driving where revs will change more often and clutch fans are more efficient for steady speed or high speed operation because as the engine spins faster to make the car faster, the fan will also go faster. I'm thinking of DK's story of his 88 cressida doing 115 for hours across texas just fine. :-p
clutch fans are temperature based, not speed based. they will not spin with the engine up to a certain point then just stop spinning faster. there may be a % slip involved but no speed limiting component in the clutch. only engine speed, clutch slip %, and resistance of air moving through it.
e-fans are also going to be better with bigger grill openings or at least potential for high airflow (chin scoop like GMs) to use more ram-air cooling. My truck with 1/2 of the grill blocked and fan off is fine carrying 800 lbs at 75 mph in 80f weather (granted I have a radiator from a car with 2x the power and 1/10 the grill) wheras I was talking to someone this weekend at the track about a friend of theirs that had to remove the bumper to his 240sx because there wasn't enough airflow for both the intercooler and radiator with the e-fan on.
on GM trucks and SUVs usually 3/4 of the noise from under the hood (especially with blazers/S10s) is the mechanical fan sucking air through the radiator.
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
mechanic, carpenter, stagehand, rigger, and know-it-all smartass
"You don't get to judge me for how I fix what you break"