I think what folks have missed in both threads is that if the character already knows their top speed is X, then it means they've survived it at least once. Else they wouldn't know their top speed is higher than what a real-world object could survive.

This points to a high probability that any character rated to go that fast has some kind of secondary power that protects them when moving at speed. OP specificed Marvel, so let's pretend both that the speed force doesn't exist and that there's no Marvel equivalent cooked up for this character.

Canonball has a protective field when he's using his power. Aurora and Northstar have canon speeds high enough that they never try to go as fast as they can because they're not sure how much damage they might take, buys are sure what kind of damage they'd leave in their wake. Quicksilver has a canon record of mach 1280, and suffers no damage from it.

What we can take away from this other than writers and editors being who decide what limits there are, is that the Marvel universe, 616 and otherwise, includes speedsters that can exceed mach 195 without dying or burning up. As such, there's no reason to conclude that OP's OP OC wouldn't have some kind of similar protection. It's akin to spidey being able to throw punches that crumple steel and shatter stone, but having no damage other than bruised or bloody knuckles. Unless stated otherwise, the Marvel default is that if a character has a feat, they have whatever protection they need to reach it without suffering more than minor damage.

Now, is OP OP? Not by Marvel standards, no. It's basically Colossus and Quicksilver's bastard child. Certainly a dangerous character, but completely beatable by dozens of heroes and villains, including less popular ones.

Nerd out