Well I've been interested in the SM951 for Windows boot, but I've asked twice now in the big thread if anyone could verify that Windows will boot from it, and was never answered. I'm not the only one who asked. I found one guy who sort of implied that he did, but it wasn't very clear. When I directly asked him to verify, he would not answer.
I did hear back two theories. The first was that Windows won't boot from an external media source, and PCIe cards are considered to be external media on a Mac, so of course it won't work. The second theory is that Windows will boot from PCIe because even if the Mac hardware thinks of PCIe as external media, all that matters is what Windows thinks of it, and Windows does not see it as external media, so of course it will work.
I was pretty excited to see your post saying you were using SM951 with Windows, but it looks like you're not there yet, so once again I'm just shy of finding someone to verify. When you get around to trying it out, I'd appreciate verification if you get it working, and if you had to do anything special to get there.