Just a thought...did you do an update or a full, clean reinstall of 10 over 8.1? From my anecdotal testing: 4 machines with update 8.1 -> 10. One was fine, the other 3 performed very poorly. Doing a clean install fixed my perf issues. The one that was fine had a almost stock (no additional software) install of 8.1 that was a few months old.