SteamOS for Apple Macs is finally here: AAA PC games get tested on MacBook Pro
(www.notebookcheck.net)
I feel that this has to be much slower. VMs add a layer of complexity, where it then still has to translate Windows/DirectX/x86. Crossover is doing that already, though I think it has to go to Vulkan before metal. Maybe I'll give this a try on my macbook later today to compare the performance.