the 85 is about 100 rpm lower than the 100 and the 85 is about 1.5 lbs lighter.
there are many pages of info but here is a quote:
"I have pretty much decided that any plane will perform better with the 85 than with the 100 due to the almost identical power and the lighter weight of the 85.
TF"
http://www.flyin ggia nts.c om/forums/fg68/17798-da-85-actual-field-results-17.html
take out the spaces and cut and paste the above
by the way i have the DA-85 on a H-9 Cap at 21.5 lbs yes yes its sweet
times are changing with technology