According to Official Guinness Records,
The highest score on Pac-Man Championship Edition is 451,660, achieved by Chris 'dragonangyle' Zupan (USA), in Tacoma, Washington, U.S.A. on 9 June 2010
http://www.bragster.com/brags/367904 NOTE: This is for a 10 minute run, and is distinct to the 5 minute record present on GWR Challengers.
For a complete list of 2010 records, please visit 2010 Guinness Records in United States.