Highest score I've seen so far that was backed up with a screenshot and is from a known skilled Pac player is 290,390 by Aart van Vliet from The Netherlands. Aart is a kill screen player on Pac-Man, holds the world record on Pac-Man Plus, and is one of the top 2 or 3 players in the world on Ms. Pac-Man as well.
The suck part is that the game kept freezing on him in these late stages. That 290,390 game froze when he still had 2 lives left.
Aart's also mindblowingly good at Galaxian (1.97 million).