It is especially for rough climbing at low speed, that the 5304 does not suit my needs. Of course I want speed and the 5304 is great for that matter, and it climbs not so bad when I can attack the hill at higher speed. The problem is that it loses efficiency and heats alot when the trail gets rough and I have to trick climb much slower.
My guess, is that I can find a compromise, running the 5306 at higher voltage, and if I have to feed it more amps it will take it without so much heating. If I can keep the speed that I do now, and get more climbing power and efficiency at lower speed, It might do it for my needs in the mountain where I ride most of the time. I want to avoid drilling cooling holes in a hub that I often ride in the mud.
That is why I will eventually end up with 2 different bikes for the street and the mountain. A steep hill can always be attacked faster on the street, therefore my 5304 with the 18 4110 will do nice with some minor upgrade to make it 100v and 80 or 100A. On the other side, my 18 4115 will make it possible to feed more juice to the 5306, to compensate for its lack of speed.
Building a 2nd bike, with a different aproach from the first, will let me figure out where I'll want to go for the 3rd.
I might want to go for a crank drive in the mountain, I don't know yet how long those hubs will stand jumping and rough driving in the dirt.