If you keep your model far from the SU origin, you will always suffer from clipping (and this "jitter" syndrome Thom mentioned). The same even if you move your stuff closer to the origin but leave any tiny bit of geometry "out there".
A solution could be (I'm just "thinking loud" now as I'm too lazy to try out) to
select all in your original SU file (with the origin away in the distance) make a component of the whole model Save (this component) as... (Context menu) open the component as a "normal" SU model (note that the origin will be close; where the origin of the component was placed) do all the modelling work if you wish, "Reload" this model/component into the original file.Certainly a couple of steps to do but it shouldn't be more than a minute and you waste much more time with suffering this way.