Looking at fps counter from standard assets, it looks to be about 3 times as fast in unity 5.5 and 5.6b1 on mac. Is this a bug?
Guess its not.
Why would it be a bug for your game to run faster on faster machines?
No, its all on the same mac. When the editor is set to pc, Mac and standalone its 3 times as fast as the editor being set to ios.
Unity added an option for mac to use a lower resolution which seems to be enabled by default in 5.5 when in pc, mac and standalone. Although, I didnt see anything in the release notes.