Okay, for my two penn'orth,
I installed Win 8 Pro about a month ago on my desktop PC. I have no touch screen. The start screen took a bit of getting used to but once I 'modified' it to my liking (grouping tiles into 'sets' of similar apps, resizing the tiles, making sure the tiles I use most are on the main part of the start screen) it all started to fall into place. I have a tile for X2 that requires one click to launch and no 'double clicking' required for any app on the start screen. The traditional desktop screen is still there, you just have to switch to it, and the installation of Classic Shell gives almost identical functionality of the original start button.
Now as for performance! Compatibility is excellent - all the programs that worked under W7 work faultlessly under W8. W8 drivers for most of my hardware is available and installed and for those that don't have W8 drivers (an old casio Keyboard) work fine with the W7 drivers. X2 performs exceedingly well with no glitches, freezes, pops etc., and latency is very low. All my VST's work fine too.
Overall the OS seems 'snappier' - it may be my imagination but programs seem to load quicker, windows open quicker, dialog boxes open and close quicker etc. I get the impression that under the hood W7 has been 'tweaked' to get better performance and the W8 interface sits neatly over the top.
One issue to be aware of - you CAN install W8 pro without needing an account or password (no-one else has access to my machine) BUT if you use your desktop PC as a normal PC for the internet, emails etc., and you LINK your social website accounts using a Hotmail, Outlook or other e-mail address to make use of the live tile updating of Facebook, Twitter etc., FROM THAT POINT ON YOU WILL HAVE TO SIGN INTO W8 WITH YOUR ACCOUNT NAME AND PASSWORD!! There is no going back from this. You cannot then create an account that DOESN'T have a password. Personally this is my biggest gripe and is the reason I went back to W7 temporarily before re-installing W8 and learning my lesson. I HATE WITH A VENGEANCE having to 'Log In' to my own computer - I know all about security BUT there are thousands of people who don't have kids or have other people who may have access to or use their computers, so in my view this is totally unnecessary. It's like having an overriding 'User Account Control' that you can't tun off!
Save for this annoyance I have found W8 a pleasure to use, even without a touch screen. 99% of my existing programs are compatible and seem to work just as well if not better under the new OS. I am not too fussed about having a touch screen, but when they become affordable I will give one a try. Hopefully, if I don't like the 'touch' part I will be able to turn that off!!