There are plenty of long, straight, flat roads around town here, where riding at 28mph would be perfectly safe. People driving feel free to go 30+mph, after all. My e-bike's assist only goes up to 20mph, which I can sustain even without assist on many of those roads. I'd guess 25mph would be about as fast as I could go with assist while still feeling safe on a bike.
I propose a new and improved e-bike classification scheme:
Class A: Bikes that can not go over 10mph via a throttle. And can’t go over 28mph with pedal assist. Or set the pedal assist limit at 20mph if you’re feeling especially conservative.
Class B-Class infinity: These aren’t considered bikes. Class A is the only class of e-bike.