Quadro NVS 420, 340.x driver, Ubuntu 16.04, 3 screens, periodic temporary freezes, rotation does not work in nvidia settings

I have recently installed Ubuntu 16.04 with the 340.x driver using a Quadro NVS 420 (rev a1).

I am experiencing slow graphic response (after turning off animations, etc, under compiz) and periodic short freezes (10-20s).

I have the nvidia-bugreport output, but no apparent way to attach here.

Additionally, it does not seem possible to set screens to rotated in nvidia-settings.

Thank you for your help,