Is there a noticeable performance difference between the Linux and Windows folding clients for a GTX 950 SC with 10 HT cores of a socket 2011-1 Xeon? I'm going to play with a dedicated box that can just fold all month but I'd like to get the max performance possible out of it. I'm very comfortable in both OSes, so may end up just popping in a spare SSD and bench-marking each, but I know there's some difference in folding speed depending on the type of WU you happen to get.

I generally see about 10% more points on the GPU clients on average.

you will need nvidia drivers.

In theory any modern LINUX distribution will work, but for most science work it seems like Ubuntu and it's variants (I prefer XUbuntu myself, though that might change when Ubuntu retires the Trinity window manager and moves to XFCE on it's core distribution) and Debian due to "how close" it is to it's Ubuntu descendent are the best supported.
RedHat is probably the next most widely supported, though they still catch flak over their non-free corporate model (oddly enough IBM doesn't catch the same flak).
apt and apt-get for package management/upgrades is MUCH easier to work with than pkgtool from Slackware, for example.
 

IBM offers LINUX on at least some of their own systems, but I'm not sure if it's their own distribution.
 
https://www.ibm.com/it-infrastructure/us-en/linux-server/ among many other links.