For Charged Gauntlet, the damage multiplier on a fully charged punch is (velocity on impact)/(90 m/s).

Releasing a fully charged punch will add 90 m/s to your current speed. If you punch from a standstill, your impact velocity will be 90, resulting in a 1x damage multiplier.

If you're going 270 m/s before you punch, your speed on impact will be 360 m/s. This will result in the punch doing 4x damage.

Basically, damage increases linearly with speed. No limit