All the R100 bikes from the mid-late 80s until the end of the production had 'only' 60 HP - these were tuned to produce more torque at lower RPMs with the trade off of peak HP, which was generally at a higher RPM that few used anyways.
The late 80s/early90s bike, while lower in peak HP, are smoother running R100 engines that the late70s/early 80s engines. I wish I had my '88 R100RT again. My 1978 R100/7 isn't a bad bike, but it definitely isn't quite as smooth on the highway, though it is properly tuned up.
1998 Kawasaki Concours, 1982 BMW R65LS, 1978 BMW R100/7