but runs quite hot, even with the free heat-sink RC Expert sent me in an attempt to resolve the problem (although that helped quite a bit).

I wouldn't really call it free as you kinda paid $ 600,- for the kit in the first place, they should have included it from the start. With the volume it seems like they are turning out they should know you'll need it and what other components that work or not. I for one has told them some...