Good grief. So you're using a multiclassed level 18 monk to try and say the movement speeds are anywhere close to reality?
Let's talk actual numbers. When people complain about movement-per-round, they aren't discussing miles per hour. They're talking about short-term, round-by-round movement in combat. A really good parallel if you want to look is the game of football. Now, I'm a big guy. I'm built for plowing over people, and the first time I ever got my 40 timed (7th grade) I came in at 6 seconds even--1 round in D&D. That's 120 feet. You literally cannot do that in D&D without pulling off a bunch of shenanigans, and I was hardly an adult, well-conditioned adventurer when I did it years ago. And again, keep in mind I'm slow; sub-5-second 40 times are extremely common among college and professional football players. These people cover 160+ feet per round without any magic or ki to help them.
3e did it better. It not only had the double-move (60 feet per six-second round for a human), but also the run action (120 feet per six-second round). All it'd take is the Run feat to pop you up to 150 feet per six second round. If you were a level 1 barbarian or monk you'd be able to cover 160 feet per six-second round (or 200 feet with the Run feat).
In my own system I went with a speed of 6 paces (the Roman 5' variety) as the base speed for a human, then added a Hustle action (minor action; varies with base speed, but +2 paces/10' for a human; can be maintained for few hours depending on Endurance score), a Run action (main action; doubles your speed, stacks with Hustle; can be maintained for a few minutes depending on Endurance score) and a Sprint action (free action; also doubles your speed, but you take penalties to defenses and alertness; stacks with Hustle and Run; can be maintained for a few rounds depending on Endurance).
Base speed is a walk of about 3 mph (30' per round).
If you Hustle, you're going to cover about 4 mph (40' per round) for a few hours until you'll need to stop and rest and can still pull of your main action (like an attack).
If you use Run you're up to 6 mph (60' per round) and can still perform an action that takes a simple gesture or a few words to pull off with your minor action. You can do this for a couple of minutes.
If you use both Hustle and Run you're now at 8 mph (80' per round), can't do anything else, but still have your full defenses and can keep it up for a couple of minutes.
If you use Hustle, Run and Sprint all together you're moving at 16 mph (160' per round), can't do anything else and have reduced defenses and penalties to notice details (you're focused on what's directly in front of you), but can only keep up that pace for less than a minute.
Certain classes and backgrounds have options to improve that speed. The fastest non-magical combo would be a skirmisher and a background that offered swift movement. Both options ramp up with level, but at level 13+ (in a 15 level game) that would put their base speed at 12 paces (60') and a top sprinting speed of 32 mph (320' feet per round).
27.8 mph was Usain Bolt's peak sprinting speed for comparison and I don't mind an epic hero being able to sprint slightly faster than him.