"I can see how it would work very well with the Nuvinci hub gears" - what exactly Nuvinci hub gear do you use? Why does it work better? What about just hub transmissions?
I've only seen these
http://www.fallbrooktech.com/nuvinci.asp on the net. They eliminate constant shifting of gears - which at which speed of 70kpm would probably tear the derailleur apart at high speeds.
Also, you would need to reduce throttle right down when changing gears with a conventional gear set.
with the Nuvinci hub and the Cyclone motor you could constantly apply throttle and have an infinite number of gears so you can constantly tweak the gears at full power to fit the terrain.
I've not seen this done before but it would be cool. (if you can manage the noise equivalent to an electric drill)
There's less moving parts to the Nuvinci than conventional gears so less chance of failure or jamming of the gears and very smooth gear changes.
Remember that the Nuvinci is a hub so you can't use it with the rear Magic Pie.
you wrote: "Some people have hooked up bigger controllers that will pump the amps and hill climbing" - what controller is recommended? Would you put a link to it here?
Golden Motor do sell a 50A controller but their website is so horribly designed in such a way that I can't post a direct link to it and there's no actual technical information regarding it.
Go to Goldenmotor.com
click controller on the left
you will now be presented with the following conflicting information:

Nowhere in the Kit building page on the GM website does it mention the controller AMP rating so you can be made to think you will get 50A when this is not the case. You get the "30A" controller.
But to add insult to injury the 30A controller is in fact NOT a 30A controller and is more like a 16A controller.
I don't know why they feel they have to false advertise like or maybe it's an oversight. Either way, it's not acceptable they should be open and honest.
I fell for this trick when buying my MP and it has fallen short of the "30A" expectations.
I don't know what the 50A controller runs at but if the above example is anything to go by then expect it to run at considerably less than 50A.
Perhaps if you ask them nicely you can pay extra and get the larger "50A" controller.
Then there is the reliability factor of the controller which from personal experience is rather poor. I'm on my 3rd one now. Two failed within the space of 30km. This current one has lasted 100km so far and with TLC I expect it to keep on going but it doesn't give out too much power for me and my hilly terrain. So I bought a LYEN edition infineon rated at 30A
From doing research, the infineon controllers are among the best in terms of delivering the "stated" amps and voltage along with providing the reliability but these are pricey unless you go with LYEN Edition controllers (some ebike guy in SF who builds them in his garage and sells them on Endless SPhere at marginal proft).
There's ebay as well but these are a bit of a lottery in terms of what you will get unless you can get recommendations from other buyers.