well that is interesting; on a 26 inch rim and 100v80amps I also get about 58mph exactly out of my 5304.
I'm 52mph on flat ground with no wind on my 5304 @ 100v 80amps. About 700 miles on that setup. I have no idea how your seeing 58mph out of a 5304 100v flat ground. Are you sure you didn't mean 5303? Or maybe I have a bumm 5304? My numbers seem to match others..? Looks like I'm going to be forced to downgrade back to my 5304..
I'll check my CA speedo calibration to be sure, but I can for sure say I get more then 53mph out of my 5304; i was recently speed trapped and they got me at 73km/h, I think my speedo said more like 76km/h but you cant know when they got the measurement. Not a lot, we are after all quibbling about 5mph total. I have one of the old non-disk 5304's, 26 inch rim with Kenda Flames 3.0 tires; the small difference could be overall circumference giving higher top speed. Your top speed will also in practice be limited by voltage sag under load, and yes that was hit going down a hill where the minimum current draw was required to go faster, resulting in the highest voltage possible for the run, around 98 volts. But I can certainly hit 90+ km/h on flat, I've done it on video. No idea why either; I'm not trying to argue with the simulator, just posting my real world results. I don't have a proper comparison between a calibrated stationary source and my CA, so I leave room in my analysis for error.
My original point was merely the coincidental comparable numbers. The wider stator and same wind should naturally make the 5403 a little slower then the 5303, right? So it would be interesting if that slower speed fit right into the groove of the current 5304, just due to coincidence.