Just basic facts & physics; @Shea N Encinitas, no salt. Been doing this biz for 14 years, so 20mph is the US federal legal speed limit for throttle only. I totally agree that if that's not adequate, then buy an ebike with the unlimited pedal assist...but you still have to pedal to get to that higher speed!
There is no standard. It is up to the company whether or not they allow users to change program settings. On the Banfang C961 controller you can adjust speed, upt to 50 KPH. If you do a conversion and use a third party controller like the Cycle Analyst virtually every parameter is user adjustable.