Same model as mine - I'm seeing ~20% CPU utilisation due to system interrupts after the upgrade. That wasn't happening prior to the upgrade. Are you seeing this also or is it just something I have installed on my SP3?
<edit> just found that the interrupts are being generated by the Intel Extreme Tweaking Utility (XTU). It seems like it is not compatible with Windows 10 yet ... :-(
In win 8.1 and the way I had it. My SF3 is operated normally, meaning fan, processes, load, etc... were normal and nothing to be alarm. With that said, after upgraded to Win 10. My SF3 with no apps open(well, discounting the background process), the load was always hover at 35-40% and CPU at 2Ghz+. Therefore, the fan would kick in and always on. That led me to investigating the background processes.
I disable indexing per ctitanic suggestion, but it wasn't it. I then started to poke around more and found the tab that says "Background apps". There are pretty much all the apps I had installed in Win 8.1. So, I pretty much disable 80% of them as of now. After rebooting, the issue with fan and the load were GONE!!! I am not now happier. The load is now between 1-3%, CPU is less than 1Ghz during idle and NO FAN.
I don't blame Win 10. I think it is really all the apps installed might need to be updated to be compatible with Win 10. I would say more efficient rather then compatible with Win 10. I will probably try to enable one or two app I want background at a time over the weekend to find out which one that don't play well with Win 10.
All in all, I am pretty happy with Win 10 now. Just need to get use to doing things differently.