I have recently downloaded the latest NV PerfKit (126.96.36.19942) and tried it on my new laptop with GTX850M (Win 8.1 64-bit).
Unfortunately, I have to report a problem in the initialization process. Namely, the function CreateContextFromOGLContext() returns NVPM_ERROR_INTERNAL (17) NVPMRESULT.
The result is the same with all drivers I tried (340.65, 340.52, 337.88 ...).
Does anybody have the same experience or any hint what might be the problem?