FYI Aspyr say the game is playable on the M370X, M380, M390, and the workstation-focused D300, D500 and D700. All of which, except perhaps for the D700, are outperformed by the 780M GTX from the 2013 iMac. These are mid-ranged mobile GPUs at best, and the 780M is a high-end mobile GPU, albeit from 2013.
Also, nVidia released the web drivers for Mac because they have workstation/professional users running Mac Pros who want to use modern GPUs (and optimise CUDA performance) in their professional applications (e.g. Smoke, Resolve), not play games. This is why it took so long to add support for non-Mac Pro systems.