This is something we have all struggled with or at least thought about sometimes. I thought Jed's case is inspiring: http://www.ugcs.caltech.edu/~alpine/wiki/Jed_Brown_Slideshow
I had the privilege of doing some climbs with Jed (needless to say it was boringly easy for him), and also heard Bruce's talk at ETH (Bruce is also a PhD in physics, probably from ETH). I tell ya, they rock. I wonder, is it that for some people this work-mountain tradeoff does not exist, some are just born with better genes?