I am using W8/C7 and have used W8/C6.5 (even used C6/6.5 with W8 pre-release versions).
Currently using C7, MR816csx, CC121 and Midex8 with Intel Extreme boards/processors and W8.
The MR successfully runs with add-on FW (TI) cards (have used two different ones) as well as with internal (Intel Extreme/TI) ports, which is a preference IMO (less stuff, less problems).
All machines are dedicated to music applications, with some used in conjunction with software development and therefore require development tools.
Windows 8 and Steinberg software rocks!