The fan actually went out and I have run it several times without it, just with the heatsink. It doesn't really overheat. I can hold onto it for some time after I run it without it hurting.
I popped your configuration into the speed calculator and it says 35mph. If your vehicle really does go 40 with that setup, then my 9XL on 4s should be doing lower 40s with a 17/36 gearing and slightly larger tires.
The timmy - Revo 3.3 MM 9XL 4s , Rustler MM 4600 3s
The ferty - Dual velineon Revo 3s, Rustler velineon 3s
I raced a MGT 8.0 after it was tuned the other day and I have alot more acceleration and a touch more top speed. I think those are good for 40mph...
This setup is only temporary. If the motor frags it's no big deal. I am going to be running the MMM combo with motor. Should be alot more efficient and run cooler which means I can gear it alot higher. I am happy with how this truck runs for now.
I might add that is has been in the 90s outside so it would run cooler on a cooler day.