Weird performance

I have been playing forza 6 apex for a while now and have had a few performance issues. my system is a core i5 6500 and a radeon rx480 and 16gb of ram, monitor at 1440p freesync.

today iam playing in medium video settings in the forza video options and the frame counter is showing just under 60 frames, then i change this video option to ultra setting and start playing again and to my amazement the game looks better as you would expect but the frame rate is now showing 82. how can this be never seen anything like this before.

another thing does any one know if these forza games run in freesync or gsync. I do find that these microsoft games now running on PC are quite a different beast to other PC xbox games such as project cars for example.