I usually keep the RPMs at 3800 on the highway.  This
is still in the green zone on the tach, for what it's
worth.  3800 corresponds to a road speed of around 100km/h,
which is about right.  Dennis Haynes says it's OK to keep
RPMs at 4000, but above that the oil temperature gets much
higher.  I don't have a temp gauge, but have noticed the
strong relationship between load and oil pressure:  If I
cruise at 3600, the oil pressure is proportionately higher
than at 3800, and so on.

My recommendation?  If I'm not in a rush, 3600.  If I'm
in a rush, 3800 or maybe 4000 for a while.  No more than
that.

tabe johnson / 87 westy