The Hercules/Valhalla will let you set voltage or phase, not both. I've just completed an offboard Valhalla into Thorens TD160 project and played with the phase cap to find the sweet spot for the Thorens motor. When you adjust the output voltage the phase angle will vary. And this will be affected by the impedance of the motor under load. So you have to choose which is more important: voltage or angle. I suspect that adjusting for exactly 90 degrees will give the smoothest, quietest running, regardless of voltage.
For the Valhalla in a Linn I guess that the phase cap of 0.22uF adjusted for 85V primary was a good default setting for Linn to achieve 90 degrees with their motor. Measuring that for dealers when the Valhalla came out would have been tricky, so a sensible "set to 85V" default was a good approach. These days any modern oscilloscope will have that capability. So blindly lowering the voltage for "quieter running" without measuring its affect on the phase angle is pointless.
FWIW with the Thorens motor 0.20uF allowed me to get 90 degrees at 120V. Smaller capacitors (0.15uF) got me 90 degrees but at Linn level voltage (85) which the Thorens motor didn't like. I'll get hold of a 0.18uF and see where that gets me.