QuakeWorld doesn't have the same physics as the original Quake/NetQuake. Basically, you can't avoid friction in normal Quake and you're running the game at a lower fps (72). ~520 ups is somewhat of a soft cap, most people probably can't go faster than that with regular strafing. There is a different technique to increase your top speeds, explained here:

Most top runners do, but they're not necessary to get a good time in full game runs. For example, the previous world record (12:17) did not use them.

Just for the sake of saying it, 480 prestrafe is pretty darn good.