My setup: Dell workstation with two quad-core Xeon processors, 12 GB memory, NVIDIA Quadro NVS 420, two Dell U2711 monitors. Boot disk is a 256 GB Samsung SSD. Photo data is stored on an internal 2TB HDD.
Until a couple weeks ago I had only Win 7 Pro 64-bit on this machine. At that time I created a second partition on the SSD and installed Win 8 Pro 64-bit on that, so now I have a dual-boot system. Programs, like CS6 and LR are installed on each OS, but data is shared, including the LR catalog.
This setup allows me to run LR and PS on both systems with the same hardware and compare performance. Both of these programs, but especially PS, is slow and unresponsive on Win 7. The difference is amazing when compared to Win 8. Truly night and day. I don't have the delays, slow rendering, etc. that I had come to live with in Win 7.
It should be noted that the Win 7 install is also new, as I just recently added the SSD and reinstalled everything on that side from scratch.
Of course, if Win 8 is unusuable, as some have suggested, then this performance boost is irrelevant. Like many others, I find the Start (i.e., Metro) screen to be a major PITA. I hate it, although I have learned to use several smart phone OSs over the years and I am sure that I could become used to the Start screen.
However, I chose to install one of several free third-party Start Menu replacements for the Win 8 desktop (Classic Shell), and I never have to look at the Start/Metro screen any more. Win 8 boots directly to the Desktop, and I have a very configurable Start menu that can look like the one in Win 7, or Vista, or XP, or whatever you want to to look/behave like. Except for the "Charms" appearing when the mouse gets near the right edge of the screen (which can simply be ignored), my Win 8 install works just like Win 7. Except that PS and LR run much better in Win 8, at least for me.
Also, FWIW, I have an Epson R1900 printer, and while Epson is promising Win 8 drivers, they are not yet available. I installed the Win 7 drivers in Win 8, and the prints I make in the two OSs are indistinguishable.
So, for those who are willing to dismiss Win 8 just because of the Start screen, consider that the Start screen can be made truly optional, and that there is more going in Win 8 than a new interface. You may see some serious performance differences.

