> I have a late 2016 and BP, and I cannot install El Capitan as it lacks drivers for the new hardware. I am able to run El Capitan in parallels, but it is slow. I was hoping to
> speed things up on a physical partition.
> I want to be able to run the old Xcode on my new Mac, So if I'm going to run El Capitan, it will have to be as a guest OS.
I got it. First of all, there's no official way to run macOS guest from physical partition. You can run this guest type only from a virtual disk. Secondly, likely you'll not get significant performance improvement switching from virtual to physical disk. Especially on SSD. It better to give more CPU cores and RAM to macOS guest to speed up it.