I'll report my results when I install it. I am in the US, and I have a first generation Gain M20i (meaning, X35 not X35+). I fully appreciate that I get a 20 mph (32 kph) with the factory default before the cutoff. 15 mph (25 kph) would only be marginally useful to me, and I empathize with the frustration of having a 25 kph limit for those across the pond.
That being said, of course I want more than 20 mph! Without assist, I can ride on the flats at 17-18 mph. With assist, even at only 42% (orange for me, the middle level), I can readily exceed 20 mph and the cutoff happens. The guys I ride with are B riders (metro Atlanta), which here means group speeds of 22-24 mph on the flats. I can no longer maintain those speeds in a group, even protected in the pack.
If I get 22-23 mph for $200 USD, that's a win for me. Based on my calculations, with a hub ratio of 14:1 (per various Mahle/Ebikemotion web sites) the motor will reach an RPM of 4000 at around 23mph, which is probably close to the outside of its operating window. Independent of other knowledge, I might expect the motor efficiency to decline at higher RPMs due to hysteresis and eddy current losses, with potential heat build up. But it's hilly here, so it's rare that I'm riding on the flats for more than a mile or two.
Which does beg the question: the rear hub on my US bike is clearly labeled that it's for North America. I always assumed the difference was in software/firmware, but maybe the gear ratio is different? 14:1 is clearly biased toward maximizing torque, and enhancing assistance at lower speeds. It would make sense for US-bound motors to have a 12:1 or even 10:1 ratio to boost "ride-ability" between 15-20 mph.
