I've been using Win 8 with Sonar X1 and a Motu 8pre, all works very smoothly. Win 8 is faster, uses memory more efficiently and has many improvements over and above the metro UI (which I quite like for apps made to use it.) Microsoft has written extensively on the engineering that went into 8, so check out their site to get the real info on performance and under the cover features. Win 8 on my wife's old laptop runs noticeably faster and saved us from having to get new hardware this year.
If you use your gear professionally, then yeah, I'd be conservative about upgrading from what's working we'll for you, just because that's the smart thing to do. For hackers like me, no worries whatsoever. imho, 8 is probably the best-engineered Windows OS to date.
Cakewalk has some good write-ups on Win8 internals in relation to DAWs on their site that makes pretty interesting reading and gives you a good idea of the kinds of changes that went into this version of the OS, and gives some perspective about MS and it's relationship with the audio industry in general.
By the way, I also have a surface tablet that's pretty darn nice too. Makes that Metro UI sizzle. On my big machine I'm almost always in the desktop, but seriously, it took all of a day to get used to the new start screen. Ymmv, etc.
Here's a really good article from Cakewalk that directly addresses the OP's question: http://blog.cakewalk.com/windows-8-a...-applications/
Here's the link to MS's blog on engineering win8. Some of the info is quite technical but you can get the drift. http://blogs.msdn.com/b/b8/