We oughta look at a few real life examples before making judgement. Obviously I agree starters play more minutes in the playoffs, I would say just model it after their IRL minutes, however the problem there is that not every player has recorded playoff averages.
Take CP3 for instance. In the playoffs last season he averaged 40.5 as opposed to his 37.6 regular season average. It's about a 10 percent increase. that's in line with what you guys have been suggesting, but can we really decide that any player, not just an all-world talent like cp3, could raise his game like that and not have to worry about wear and fatigue.
I also think a relevant point here is that by the end of the season players are in much better conditioning, so a sudden spike would affect them less than, say, the beginning of the year.