These are tips on improving the performance of your NURBS models.
Avoid using point curves and point surfaces. These are slower than CV curves and CV surfaces. Use the point forms only when you need them for construction; for example, when you use Curve Fit to create a curve that interpolates specific points.
Use Transform Degrade to hide surfaces while you are moving, rotating, and scaling NURBS sub-objects. The shortcut Ctrl+X toggles this option.
You can use Ctrl+X in the middle of a transform, to turn on degradation if things are happening slowly.
Turn off the display of dependent surfaces while you are creating new dependent surfaces or moving, rotating, or scaling NURBS sub-objects. The shortcut Ctrl+D toggles dependent surface display.
Trim holes only when you need to. For example, when you connect an arm to a torso, you don't need to create a hole beneath the arm, as it won't be visible anyway.
You can also speed up performance by turning off the Display Trims toggle. The shortcut Shift+Ctrl+T toggles trim display. The trims still appear in renderings.
For symmetrical models, create only half the geometry, and then mirror it. You can then use a blend surface or ruled surface to connect the two halves.
Restart Autodesk VIZ when performance begins to slow down. If your NURBS model needs to page, then working with it for a long time causes performance to slow. If you notice this, save your work, close Autodesk VIZ, and then restart.
When you use texture surfaces, use the Edit Texture Surface dialog (click Edit Texture Surface on the Material Properties rollout) to rebuild the texture surface with the minimum necessary number of UV rows and columns.
Every type of surface is faster if you can make it independent.
Set the surface approximation for viewports to use the lowest possible resolution. Set the renderer to use higher resolution, and turn on View Dependent for the renderer so objects far from the camera render more quickly.
You can customize and save surface approximation presets by using the Surface Approximation utility. This utility also lets you set surface approximation values for a selection set of multiple NURBS models.