You could try setting sv_fps to 125

But any way, even if you managed somehow to get the exact distance jumped, it wouldn't work correctly for gap jumping.

I found out that the movement of the player in the air depends on solid objects they are flying by. I used my .cfg jump script for various gap distances, and I noticed: the greater distance it was, the bigger value my distance-meter would show. Although jumping with a script is supposed to be pretty much the same regardless of which gap you jump over.

That there problem limits the use of the distance jumped check.