Just installed the latest NVIDIA beta driver – 361.18 – and it is now OK with Plasma and KDE5..

Release notes and download link here:   http://www.nvidia.com/download/driverResults.aspx/97474/en-us

Notes include: ”Fixed a bug in the EGL driver where a mutex was unlocked more than once. This triggers undefined behavior, and in particular, if lock elision is enabled in glibc, may result in a segmentation fault.”

* ”lock elision” is not a typo – it is described here:  https://lwn.net/Articles/534758/

Robert Gadsdon.   January 13, 2016.