For those that have upgraded or considering upgrading, the Windows 10 forum has lots of good info and help.
www.tenforums.com I have my 8.1 upgraded and after Roland got their drivers upgraded everything is working OK, including my VST add-ons such as Ozone 5. iLok is working OK.
When I record, I disable the NIC (Ethernet adapter) so I'm off line. The prevents possible interference to Sonar from network activity.
I'm in the Windows "Insider program" and have had Win10 Preview (Beta) versions for quite a while. The only thing that put a kink in things was my Roland Studio-Capture and Octa-Capture installed OK in an early Win 10 Preview version but in the final 10240 version they would not install. I had been going around "fat dumb and happy" assuming they were OK. Apparently the early Win 10 Beta versions were more Win 8.1 than 10 and Roland drivers did install and work. I never checked them after that until 10240 version (the "final" version).