"The combat speed of that faster character is assumed to be equalized to the combat speed of the slower character. Every other speed the faster character has is reduced by the same multiplier. This includes the speed of any attacks, projectiles, reactions, perception, flight etc."
Basically if we have someone with Mach 10 reactions and combat speed, but Mach 20 attack speed with whatever. So when speed is equalized in this case, the attack speed will still be two times higher than equalized speed of the combatants. Speed amp techniques are assumed to grant the same percentile of increase to a character's equalized speeds, as they would to their usual speeds. So if someone can make themselves 10x faster, they'll still be able to make themselves 10x faster.
If a Supersonic (Mach 2) character has a speed amp that scales them to Hypersonic+ (Mach 10), that means they can amp their speed by 5x in a versus thread where speed is equalized.
"However, any speed equalized match, in which a major reason a character loses is due to having a disadvantage against some speed value they usually wouldn't have a disadvantage against, may not be added to profiles."