anantech.com ran their benchmarks of Intel's new Kaby Lake processors on Windows 7 SP1. Remember, Kaby Lake has no Windows 7 support from Microsoft, same as AMD Ryzen (not to mention Skylake, as only certain OEM machines received Skylake updates), and remember that AMD demonstrated Ryzen basically equals performance with the i7-6900k. Could it be that AMD Ryzen will suffer negligible performance loss on Windows 7? Kaby Lake sure didn't see any, and still clearly spanks the 8370. That's reason enough for me to get excited about Ryzen again (and possibly for Microsoft to get scared again as cutting support for Windows 7 and 8.1 isn't going to drive people to 10).
I'll certainly be happy if I don't have to install Win 10 to use new hardware. But I think when their saying you'll need Win 10 for those cpu's it doesn't mean that there will be a performance hit right across the board. Some area's of performance might be down, some might not be affected at all. If I knew I might get better OVERALL performance from a new cpu with Win 7 I would probably get one.