Yeah.. I put it all down to ESXi 6.7 - have never used that version before, but have used 6.5U2 and that was fine.
6.7 is very very odd. Performance all over the place.
Main reason for running VMWare is that I run an SSD in the ODD bay, and 4 x 4TB drives in the bays. This means that to boot from the ODD into Windows 10, then I need to use a SD card fudge. That works great, but every time there is a major Windows update then it fails to install because it thinks I am trying to install onto a USB drive. Have to remove the drives in the bays, boot into windows, update windows, redo the SD card and then put the drives back into the bays.
What a faff!!