Clipping Plane with Show Fills still very slow

Display performance becomes so low that Rhino switches to wireframe mode when panning and zooming. Huge difference between show fills on/off.

Also, faces are not cut correctly:

And still no display feedback when creating objects.

testmaxspeed times:

Shaded, no clipping plane: Time to regen viewport 100 times = 9.44 seconds. (10.60 FPS)

Shaded, Clipping plane on, Show fills on: Time to regen viewport 100 times = 24.14 seconds. (4.14 FPS)

Shaded, Clipping plane on, Show fills off:Time to regen viewport 100 times = 4.89 seconds. (20.45 FPS)
(better performance because there’s only half of the model visible, the other one being clipped)