[ubuntu] Wacom Cintiq 13HD - Slow, laggy

Hello,
I'm using Krita with OpenGL selected in the settings.
The tablet works great before the renders are applied (so, the ink appears quickly as normal when there is no pressure sensitivity in action) but as soon as pressure sensitivity kicks in it's laggy and super slow. Unusable slow.

Is there any work-around out there for this?

I'm on Ubuntu 16.04.
My GPU is a NVidia GTX 750; using X.org drivers.

Thanks for any tips.

Edit: GIMP works fine. It's pointing to being a Krita problem...