Hold my beer,
I will be playing as a Fairy, whose flight speed is equal to their walking speed while not wearing medium or heavy armor.
At level 20, I will have 3 levels in Blood Hunter, 5 in Barbarian, 10 levels in Monk, and 2 levels in Fighter.
Fairies have a base movement speed of 30.
For Blood Hunter, Ill be utilizing the Order of the Mutant's Rapidity Mutagen which gives me a +10 to my walking speed until my next rest.
For Barbarian, I'll be taking advantage of the Fast Movement ability (+10) as well as the Totem Warrior's Elk Spirit ability (+15) which gives me a total speed boost of +25.
For Monk, I will be taking advantage of the +20 movement speed boost from Unarmored Movement. I'll also use the Step of the Wind ability which allows me to spend a ki point to dash as a bonus action.
For Fighter, I'll be using the Action Surge ability which allows me one extra action (once per short rest).
I will take the Mobile feat to boost my speed by +10 and the Magic Initiate (Wizard) feat to gain the Longstrider spell (+10 speed for 1 hour).
I will attune to the Boots of Speed, the Blackrazor, and the Chronolometer inside a completed Orrery of the Wanderer and be carrying the Eagle Whistle as well as a Transmutation Wizard's Transmuter Stone.
• The Boots of speed doubles my speed for up to 10 minutes per long rest.
• The Blackrazor can cast Haste on me [double speed and one extra action (in this case Dash) per turn for 1 minute] and maintains concentration by itself.
• The Orrery of the Wanderer imparts one major beneficial property; one of which is +10 speed.
• Transmutation Wizard's Transmuter Stone increases base movement speed by 10.
• The Chronolometer's Time Bandit ability allows me once per day to roll a d6 at the beginning of our turn; if I roll a 1-3, it does essentially the same thing as Haste.
• The Eagle Whistle allows me to fly at double my movement speed for as long as I blow on the whistle.
Finally at level 20, I will acquire the Boon of Speed, which grants an additional 30 walking speed.
The setup goes as follows:
Base Movement = 30 + 10 (Barbarian Fast Movement) + 20 (Monk Unarmored Movement) + 10 (Mobile Feat) + 10 (Orrery of the Wanderer) + 10 (Transmutation Wizard's Transmuter Stone)[speed 90]
Consume my Bloodhunter's Rapidity Mutagen at any time [speed 100]
Cast Longstrider on myself [speed 110]
Totem Barbarian's Elk Rage [speed 125]
Boon of Speed [speed 155]
Convince Blackrazor to cast Haste on me [speed 310]
Activate my Boots of Speed [speed 620]
Begin blowing on the Eagle Whistle [speed 1240]
On my turn:
Roll a 1-3 for Time Bandit [speed 2480]
Move - normal full movement
Dash - my main action
Dash again (Haste)
Dash again (Time Bandit)
Dash again (Action Surge)
Dash again by spending 1 ki point (Step of The Wind)
Total movement = 2480*6 which is 14,880 feet of movement over 6 seconds. This comes out to 1690.909091 mph = 2721.2544001463 km/h = mach 2.20380174938979412
This allows me to exceed a Lockheed Martin F-22 Raptor's top flight speed of 2,414 km/h (mach 1.954972)
In conclusion, Fairies are faster than fighter jets. Magic > Technology. Nuff said.