I run my 1.9 at 55 mph (no power steering or air).  141K miles on original
motor and no major repair...yet!  When were on the road it is usually full
of camping gear, two kids, dog and wife, ...and usually a few cold ones in
the fridge for when we "eventually" get to our destination.  Probably lots
of debate about your question.  However, it always puzzles me when I read
about Vanagon with an engine rebuild between 90-125K.  Is it because of
poor maintenance, over working the engine, poor driving skills, I do not
know but I expect to get alot more miles out of mine before I need a
rebuild...but only time will tell.

Pascal
'84 Westy