The amount of power e-fan(s) pull at lower speeds is very minimal when considering the load against the alternator. On both my trucks I run e-fans without a problem for over two years here in the Texas summer... which resembles hell in some aspects in temprature.
Now I'm using a variable speed fan controller from Flex A Lite, it's rated at 40A and has four heat sinks on it. There is a 25A version with two heat sinks also. Now the key with this controller is to run all 10awg power wire from the controller to the fan and whatnot. Prevent burn up.
Next, if you have the extra dough... get a better controller from
www.dccontrol.com It's about $90 as opposed to ~$60. But it's a more solid unit. It's what I plan to upgrade my VSC's to in the near future.
Both controllers are variable speed, meaning they will soft start the fans at 20-50% power when they click on (20 for the DC, 50 for the VSC) and are fully adjustable from ~160° turn on to well over 200° both in deg Fah. AND you can also wire up full ON or full OFF switches to either units to turn them off when you choose.