Yep, for file access alone, VirtualBox is an order of magnitude or so faster for me. Lumped with all other processing in our test harness, we’re looking at a ~2.3x slowdown.
Important note, though, is that osxfs is not mounting /Mac on my containers and may not be working at all. If osxfs is used for volumes specified with -v on the command line, and falling back to some slower method if osxfs isn’t working, then that might be my underlying issue. Shot-in-the-dark guess on my part, though.