I'm only reasonably fit and in my late 30s, but the badass dongle is more than fast enough for me on an otherwise standard haibike sduro trekking.
On flat with no wind 30mph is fairly easy physically, 35 for short bursts, 40 if really putting in a lot of effort.
Even though 30 is fairly easy, I only feel I can go that fast safely maybe 10% of the time and my average speed is 15 despite a fairly open commute. Braking distance / visibility are the main limiting factors.
I've only been overtaken once by a bike in months. At 30mph a more confident Kalkhoff whizzed past - am guessing at over 40mph without much effort so guessing a bigger motor.