What is the best/fastest way to rip and convert a Blu-ray Disc on an iMac?
So I found a solution, just not a short or elegant one:


Install bootcamp on the iMac
Install Windows 10
Install dvdfab.


At first dvdfab did not want to work with the GPU (AMD Radeon). Turns out that the graphic drivers bundled with bootcamp were too old, but there is no update from Apple. http://bootcampdrivers.com has newer driver packages for the mac / AMD GPU.

I had to follow a long set of instructions to install it, including booting the Windows machine into Safe mode. In the end, everything works as it should, and Blu-ray conversion time is now around 40 minutes!

As converting Blu-ray movies is not something I do everyday, I can live with this solution.