You asked us:
"We are considering setting default game size to 10 players. We hope this will mean more games and less idle time and less lags ingame. What do you think?"
I voted for 10 (5v5) or less, because i think its better (due to lagg and idle time, as you told) than much more players, but my suggestion you can see following:
Why 10 Players and not 12? If you got 10 Players you can only make 2 or 5 even teams. If you set the default game size to 12 you could make 2, 3 and 4 teams.
What do you think about that suggestion?
PS.: Im sorry if i made some grammar mistakes, hopefully you understand my post regardless.