Well that didn't take long. Thursday complaints hit the web about NVIDIA's most recent mobile driver releases, which once again disabled overclocking on mobile GPUs, and yesterday afternoon the green team already issued a hotfix for this issue!
This is a GeForce Hot Fix driver, version 353.00 that addresses the following issues:
Fixes a regression that prevented overclocking the GPU on some GeForce Notebooks
Meanwhile the Catalyst 15.5 Beta driver AMD promised would arrive this week is still missing in action. This release should contain performance enhancements for Project Cars & The Witcher 3.