911 lowering, rear height adjustment

I am preparing to lower my '86.

Does anyone know how much the ride height will change for each spline I rotate the torsion bars on the rear (both inner and outer)?

Also, while I'm at it I plan to replace the bushings on the rear spring plates. The car will be used on the street. Are the plastic ones unacceptably noisy if you lubricate them?

Thanks
Chuck