Marty would not be the first athlete to believe something about his play that wasn't entirely truthful. I see very little evidence to support his claim, and even less to support 65-70% being a good split. I'm not convinced a drop to 50% is going to kill his mojo. That's what, 6 games over 4 months?
And if anecdotal evidence is going to suffice, he sure started like gangbusters having having not played in 7 months and having a very short training camp. Then he kept playing, which should be advantageous, and has played 75% of our games and has not played as well (although with small sample size + some bad team play). I'd love to take an actual look at this issue so we don't have to deal with the same arguments, but i'm going to have to find the time and remember my stats classes.
Basically, if marty plays better with more games, then why 65%? He clearly has been under performing the last two seasons receiving such a workload. If he needs to play more to be better, play him more. If he needs to play more to be better but this is counteracted by fatigue, then we have an issue and maybe having a 41 year old goalie is a problem because right now we're receiving below-average goaltending from him (our starter) and have for the last 123 games (10% of his career).