I ended up getting one of the SM951s off that guy on eBay. That's the only way to get one right now, everywhere else won't get them for a few months, looks like eBay dude was pulling them from Lenovo ultrabooks and that how he had stock.
Windows 7 should work, I only tried installing 8.1 but it installed in AHCI mode instead of NVMe so 7 should install also.
Can't really speak to the speed, I'm got it working in the M.2 slot on my Gigabyte X99M Gaming 5 but that's only a x2 slot so I couldn't get full speed. I tried using a PCIe to M.2 adapter but the BIOS doesn't recognize it as a boot option so I couldn't test speed.
Honestly, compatibility is going to be a major issue with this drive so I'd hold off for a consumer version or at least until they're more commonly available so motherboard makers can get BIOS updates to support it better.