Hi Mike,
When you say:
with Vmware Fusion both are generally slow and quite inconsistent in the time they take
Can you give us any numbers? Are we talking seconds, minutes, more?
Slow is a very relative number.
Re. the issues with APFS, those are supposedly solved. But perhaps there's an edge case that you are bumping into.
You can actually test that by creating a HFS volume on top of your APFS file system. (Disk Utility -> File -> New Image )
Make it large enough to contain your VM + RAM + additional size for snapshots.
Then copy your VM into that image. (yes, copy, not move as you're experimenting. Note though that you should answer the question "did you copy or move" with move not copy as otherwise you will have to reactivate Windows 10)
--
Wil