I once flew a near new U206G in the early 1980's that had only 300 hours on the clock and it could not get above 125 with a load on. This thing was a total dog from the day it was made. Yet a 1970 vintage U206F that I flew a lot on ATO would always do 135 with a full load. All of the other C206 aircraft I have operated fell somewhere in between.
I think that 185's are the same, some are born fast at the factory. There are a few that I can keep up with in an early O-470 J C180, and some that just blast away like a dog shot in the a*se