Some interesting thoughts in here. According to RV builders the no.1 reason for side radiators: SPACE.
A rear radiator will move the engine, transmission and axles forward 18-24 inches. Move the radiator to the side and everything slides back. Very important when above 9 liters.
Both will cool just fine. Rear radiator coaches have a larger radiator to make up for the warmer air used during cooling.
According to Freightliner my coaches fan can draw up to 60 hp on high.
Here is from a Cummins PDF.
The typical on-highway fan run time hits a year round average of 5-7%. It takes between 10
and 70 horsepower to drive the cooling fan. An inoperative fan clutch, faulty thermostatic
switch, low coolant level or other malfunction that makes the fan run longer can take a big
bite out of the fuel economy of the vehicle. Cooling system maintenance can have a
significant effect on fuel economy.
Table 5: Typical Heavy-Duty Fan Power Requirements
RPM ISM (HP) ISX (HP)
1100 9 10
1300 14 17
1500 22 26
1700 32 37
1900 45 52
2100 61 70
At 1450 rpm, cruise operation, the fan being locked on can cause an 8-12% mpg penalty
(assumes 225 hp road load).