Pulling constantly is a bad idea because the chamber pressure will vary with the amount of vaporization caused by heat input. If chamber pressure rises, boiling point rises and wood temperature rises. Cavitate enough and the pump is junk. As far as drying time, I'm not sure. If everything else is under control, drying rate is directly proportional to the rate that we add heat.
Quality is the big question.
I don't believe that there is an optimum pressure and hysteresis that will cover all species and thicknesses. It is possible to achieve high moisture removal rates with constant pull vacuum drying. You need active control of pressure and temperature in the vac kiln to keep deviations within sufficiently narrow margins. The MC gradients are controlled using a gradual decrease of pressure as drying proceeds, in much the same way you'd do with the RH in a conventional kiln. The net effect is negative compared to continuous drying.