There is no performance penalty or from what I have seen no gain in performance. The only penalty is a steep learning curve. Since they are talking Windows 9 next year you can look on it as not an important step or as a necessary introduction.
I use Win7 (PProCS5) and my wife uses Win8.1 (non-video, but a house design CAD program)
Once you get past the icon filled start screen (and there is an option to go directly to the old style desktop) the OUTWARD look and operation of the two is pretty much the same
There are supposed to be code improvements in Win8 over Win7, but if you are happy with Win7, you "probably" don't need to change
One thing... you MAY need to use different device drivers to work with Win8 compared to what works with Win7
The performance is better on Win 8 over Win 7 by a small percentage right now. The Video caching is far greater and the storage performance is better. If you can get past the interface changes then Win 8 has a much higher potential but the workflow can drive many crazy.
>If you can get past the interface changes
From a monthly newsletter published by http://windowssecrets.com/
Right-click the Desktop taskbar, click Properties, select the Navigation tab, and then check the box marked “When I sign in or close all apps on a screen, go to the desktop instead of Start.” With Win 8.1 Update, the system installer scans for a touch-sensitive screen. If it doesn’t find one, it checks that box.