90% of the wear in a diesel engine occurs within the first ten seconds of start-up (the proverbial "dry" start) which is why over the road trucks commonly log well over a million miles before rebuild (many run nearly 24/7 throughout their life.

I've seen diesel irrigation pump engines run 24/7 for six months at a time and do it for years (but they only started up 10 or fifteen times in their life. That's why pre-oilers are so popular on this type of engine - while not a perfect solution they do prevent a lot of bearing wear etc. ...but yes, I would think 350K hrs with no wear a bit optimistic

I often cruise at 1800 to 2200 rpm, but always run close to max for the last thirty minutes to an hour before shutting down. Good maint is the key and Bruce outlines a very good regimen below.