My 497 was in a 3 player game with one good player and one moderate player.
To score 497 points in a 3-player game is fantastic. It's almost as good as scoring 617 in a 4-player game. Having an extra round playing the 4-player game is huge...as you can score an addition 150 points or so. Typical great scores in a 3-player game would be in the low 400's.
To score crazy like 617 usually requires other players committing game "sins"...like throwing away the 1-engine and let someone with a lot of engineers to score big points with it as a factory 2-3 times, or not taking the 9-train/factory and let someone take it as a factory.
In my 617-point game, I had 2 9-factories and scored like 60 end-game points from them.