Hotter bobs (can't believe I just said that >_<) lose mental and physical faster, whereas cooler bobs are better. Therefore, normally, cooler bobs are better at endurance races while hotter bobs are better at shorter but harder races.
Hotter bobs are also better at overtaking, whereas cooler bobs need coaching or only overtake at clear openings. Hotter bobs are also better at getting to first place, but worse at maintaining first place compared to cooler bobs. Cooler bobs, on the other hand, find it harder reaching first place, but find it easier maintaining first place.
I suggest having both types of bobs for different races. Hope that helped.