If the speed limit is too slow for you on a MUP or commuter path, then only use the commuter path to link yourself up with faster riding.
When I ride road locally, I'll take maybe 1/2 mile of MUP to link to another part of town. I usually take the MUP uphill (slower) and take the street downhill (faster, often equal speed as cars). That's an option if you MUST go faster.
I think people underestimate the lethality of a head on bike crash. Had a parent at the preschool my wife works at stay in the ICU for nearly a week after an "over the center line" head on accident on a local trail because someone was cutting the corner speeding.
If you like road and want to speed around safely, bother to get up early on a weekend. I live in a major population area and at 6AM on a Sat/Sun I can bomb the 4-lane boulevards and not come across a car for long stretches of time. Roads jammed with 15mph car traffic during rush hours.
Also, for commuting by bike, same as speeding in a car.........you actually don't save any meaningful time. You only do so if it's a super long vacation trip. Not a 20 minute commute. Wow, you saved 1 minute! Woooo hoooooo.