I took it out for a run today, first giving it 50 volts, then giving it 66 volts. At 50 volts, it was OK, nothing to get excited about. But a 66 volts!
I ran it from 16s of Lipo batteries, which gives a possible maximum voltage of 67.2 volts. On the flat, it was very nice, but it really shone going up the steep hill at the bottom of my road. At 50 volts, I had to pedal a bit to help it get up, but at 66 volts, it winched me up without any help. The downside is that this eats up more power, but since the bike carries the weight of the batteries, that's cool.
Speaking of cool, the motor got a bit warm. So I added a thermometer with the sensor next to the motor - I'll be able to keep an eye on the temperature on long rides. I also removed the left pedal and gave it some oil, so now it turns freely. Experience tells me that this will only be a temporary solution, and I'll have to replace it.