Just ran some side by side tests. BTW, my Win10 install was from the Windows 10 Free upgrade option.
Scenario:
KSFO HD by Flightbeam, all sliders maxed, ASN live weather, then OPUS live weather in separate tests, REX Essential textures with Soft Clouds. No ORBX enabled for the test. Also tested REX live weather for function with no issues.
FPS in P3D v2.5 and 3.0 were close with 2.5 around 25 FPS on average and 3.0 making 30 FPS. This is better than the same setup when I ran Win7.
For what it is worth, I am noticing that P3D 3.0 has not given me an OOM at SFO after quite a few flights. This is not the case in 2.5, which seems to OOM virtually every time I try identical flights.
All in all, my system is operating more smoothly with better performance in Win10, but every system is different of course.
I'm sorry I can't offer more info on P3D 3.0 without ORBX patches for NCA etc. I think 3.0 will be a much improved simulator from previous versions when we begin to get compatible addons.
Hope this helps.