The 107 is a great long-distance driver being a little longer and
heaver than the 113. The low profile and extra length and weight let
it pass those big trucks with only the slightest wind buffeting, and
cross winds on overpasses are not even noticeable. The 380SL has 155
HP and is ok for normal drivers. It will keep up with any traffic on
the highway but don't expect to blow away anything from the stoplight.
I would prefer the 280 to the 380 for the power and, IIRC less weight,
(and the 500 to anything else in a 107). The extra power will not be
too much. I get about 20 mpg in a 380SL and would expect a little more
in the 280.
There is a risk driving an older exotic car long distances. When I
lost an alternator in Cortez, CO (SW corner, pop. 8000) on a Sunday
morning, the two auto parts stores there just did not carry a
replacement and I had to be home 700 miles away by the next morning.
(the Autozone guys spent a LOT of time trying to find something that we
could make fit but didn't - we limped home on an extra battery and
charger). Of course, your long trips might be in more populated areas.
Go for it.