One thing about the goalie fatigue factor, it's also dependent upon the goaltending style. Butterfly goalies rely more on athleticism, acrobatics, quick movement, reflexes, dropping down for the shot, etc. and I'd figure it's more tiring than for a goalie who relies more on the positioning and other technical attributes. If not managed properly it may wear the goalie out over the course of the season.
Marty Brodeur was a largely butterfly goalie when he came into the league, but with age, perfected the fundamentals and became more of a stand-up goalie. I think that kind of adaptation helped him maintain his endurance and stay competitive even past his prime.
