One of the best ways to gather data on this is to add two questions to all tournament score sheets:
"How many turns were completed?"
"Did the game end by random game length roll or by finishing turn 7?"
This can really help gauge whether enough time is being allowed for a given point size.
As to the original question, I'd say 750, maybe 1000 with experienced players. We did hour and fifteen minute rounds for our 1,000pt invitational tournament and that seemed to work well, though in round 1 a couple of people hit the limit early (high model count and I think they weren't fully awake/warmed up).
