I have the coaxial bike, that means it has the 4kw motor integrated. The motor is the same general design as the 3kw but with a ~30% longer stator that equals ~30% more torque. So the motor is wider. The gearbox is the same and the efficiency shouldn't be too different. It does not run a lot cooler than the 3kw from what I've read, but people who have both say its quite a lot more powerful and fun.
As people are already running 60A on the 3kw cyclone I would say you should keep it at that and enjoy more torque and reliability from stressing the 4kw one less.
The 60A controller is the same as the 40A with some solder on the shunt. Google 'solder shunt' if you wanna know what that is. It is a home made procedure. One good thing is the new controllers now have 100v caps instead of the old 80v ones, that means you aren't stressing them too hard by running 72v nominal (84v peak).
Vs the Ascent the biggest difference is it has a 6:1 internal reduction and it only needs to spin 700rpm on the outside on 72v(4200rpm internal). The tangent has 20:1 but spins 12500 rpm internal and 625rpm on the outside on 52v.
Other difference is price, obviously. The 4kw should cost about 10%, so if you burn up or it does to water damage/condensation you pay $200 and you are good to go.
You would expect the ascent to have much better machining tolerances but honestly, the cyclone draws 250w full rpm without load and the ascent advertises 200w. This doesn't scale linear with load either.
The cyclone controller has a bluetooth app that has tons of useful features like rpm display(different than speed), limit current, cruise control, etc..