Define "fast" 'cause until you do not much of what anyone suggests is going to matter. As for Windows 7, I've got Windows 7 working perfectly on a Kaby Lake laptop (Lenovo Yoga) that of course everybody at Intel, Microsoft, and Lenovo tell me "You can't do that, Windows 7 won't work on that machine..." and I like other people that know better just laugh in their faces over it.
Fast as in data processing for tasks like 3D rendering, fast as in high framerates for games, fast as in encoding speed for video data, etc.
I agree anything new is not going to guarantee support. I suggest you try and get your hands of windows 10 ltsb as it reminds me of windows 7 in some regards.