Going up hills is not about horsepower (watts), it's about torque.
My Panasonic is a 350 watt drive. Put my internal gear hub in a low gear and it will out pull my 500 watt Heinzmann hub motor I have on my Baria. There is no contest. Hub motors have a 1:1 drive, that's it. Run that through a hub one can gear down and what you get in return is torque. Lots of it; so much so that on my Panasonic I cracked a few hubs because I was out torquing them (disclaimer--my Panasonic is attached to an Xtracycle and I out torqued the hubs when loaded with over a hundred pounds of cargo).
Difference between torque and horsepower.
Torque refers to the amount of work a motor can do.
Horsepower refers to how quickly an motor can perform.
My Acura has a 200 horsepower engine. My Massy Furgson tractor has a 35 horsepower engine. My tractor can quite literarily drag stumps out of the ground. The Acura has nowhere near that pulling force. The Acura can go faster, but can't pull a load anywhere near what my tractor can. Bring your car to a full stop on a steep hill, put it in its top gear and let the clutch out. It'll stall because it has insufficient torque to move forward. Put it in first and let the clutch out and up the hill you go. You haven't increased the horsepower by gearing it down, you have increased the torque.
Oh, I spoke to SaraLou via email the other day. So far she has not had any issues with her Klakhoff. The only maintenance so far has been pumping up the tires and putting the bike on its charger. You are going to find that Kettlers have similar performance. Both companies use high quality components. Panasonic will not license their motors to companies that use lower quality parts.