FYI I'm now running my Tongxin @ 63v (15s lipo) and I've set a 12a limit in the controller which see a peak wattage of 725 on my Turnigy meter.
The bike cruises @ 25mph and on my 18.5mile round trip commute I'm using 7Ah from my 10Ah pack averaging 21.5wh/mile.
Hub has just passed the 800 mile mark.
I'm very careful with the hub - I never use it from a standstill and I'm gentle on the throttle to ensure I don't induce clucth slip - which I believe to be the primary cause of the ring breaking in Tongxins. I don't have any hills where I live (coastal resort in the UK) and 7 miles of my 9.2mile one way commute is solid cycle path with no traffic control (so no stopping and starting) and only two junctions after that. This no doubt is helping prolong the life of this motor.
We'll see how much longer it lasts at those power levels