I ran the same RPG game at different conventions, one was a hometown convention (Winter War) and the other GenCon. Both were 4-hour slots, both played with 6 people.
However the local con had 3 18-20 year olds who apparently had $$ to blow and time to waste as the rogue wanted to appraise everything he saw (including door frames, window frames, and frescos. Then tried to take it all with him.) the Paladin played as though he was CN and the third guy played a barbarian (pretty well as he probably had the same INT as the barbarian). The other 3 guys, who were all over 30, RP'd great and it was a struggle pulling half the party through the adventure.
The GenCon game which had the same description as the Winter War game had 6 guys show up and it was a great experience, everyone had fun and RP'd their characters well.
The local con was such an effort that I don't know if I'll ever run another game there, however I would have no problem running another GenCon game. I guess I got lucky at GenCon.
I go to GenCon to try out new games or play in long running events (such as NASCRAG), so I feel that if I goof off or jerk around with the game, then I'll never know if I like it or not. I have too much respect for the other players who paid money to attend the game, to throw the game.