Maybe the correct question is: how old are you?I've always wondered about this... What's the life expectancy of an Airweight?
Why? 'Cause you're MORE likely to keel over at an advanced old age than you are to 'wear out' that Airweight in your lifetime, JMO.
But, if ya WANT the 640 Pro, and are willing to the extra $$$ for it, far be it from me to 'argue' that choice.
Full disclosure: LOTS of great wheel guns out there, Ruger being high on that list. But personal preference for 4 decades has been S&W.
Have had more than one S&W magnum (Mdls. 66, 686, 29, 629) that have had thousands of full-boat magnum rounds down range, per year, through 'em. Never had one 'wear out'.