Update: this does not seem to be necessary in OSX 10.12 onwards.
If you have a Mac VM running as a guest on a non-Mac host (Windows in my case) you might experience some serious lag and graphic glitches like I did. Fixing it was pretty easy by disabling "BeamSync" - the Mac-equivalent to VSync if I understood that correctly. Anyway, you don't need it for normal Mac usage (i.e. no videos, games, etc I guess), so download "BeamSyncDropper" and keep on using your Hackintosh efficiently :)
You can download the tool + read instructions on how to use it here: http://www.tonymacx86.com/threads/beamsyncdropper-tool-to-disable-beamsync-permanently.92201/page-2#post-666095
PS: Mac VMs are great for developers who only develop for iOS if they really have to! ;)