[andrew wilkinson photography]

I have a similar issue with slowness in moving facial points, using highest maxed-out spec iMac.
I now find it better to deselect ALL faces, then select them manually. This seems to work in real time, seems more accurate in placing the points, so that when the face outline is rendered, it requires little or no adjustment.
I think it is quicker in overall time, but certainly a much more satisfying workflow