I've been summoned!
So, here's how I see things, based on my experiences. Do note as well that now that Sony have updated the console, you will now always be getting Trueforce on the G923 (whereas previously, if you had the wheel already plugged in when you first started the console, if you started a Trueforce game then the wheel would not be in Trueforce mode).
Max Torque
Set it wherever you like - at any setting with G923 and Pro Wheel you will not get clipping. This is because part of the benefit of the Trueforce interface is that the developer knows the torque level of the wheel and (so far) all developers who have support Trueforce have reserved the peak torque of the wheel for peak torque effects, such as bumps, kerbs etc. With the Pro Wheel you can see this because of the OLED screen that it has - steer into a hard corner at high speed with the Max Torque set to 10, Strength on the wheel at 11Nm and the torque meter on the OLED will show around 7.5-8Nm.
Sensitivity
As the scrolling text at the bottom of the screen in GT7 says, this changes the feeling of the wheel as you turn it from centre and makes it more responsive to forces. I think of it as changing the steepness of the force curve that they apply - 1 has a lower slope force curve, whereas 10 is very high. Personally for me, 1 is the generally the way to go because it feels more natural in the vast majority of cars. You can ramp it up a few notches for road cars, but the second you drive anything with downforce you're going to quickly run into oscillation problems, because that steep centering force curve and the overall heightened response of the wheel to forces means that it's going to be constantly trying to move. Have it set too high and the cars just feel too robotic for me. Again, outside of the oscillation issue I mention with the higher group cars, this is personal and what works for one person might not work for another.
Vibration
Unfortunately not accessible from the pause menu (only the options on the World Map or pre-race screens), this one is essential for Trueforce-enabled wheels because Polyphony use this to control the vibrotactile (or Trueforce Audio as we refer to it) level. Totally personal preference here, but I would say that anything over 75 is going to be very noisy. On the G923 this will result in some big vibrations, depending on what the wheel is attached to. As always, my recommendation for where to set this side of Trueforce is always to make it subtle and not overwhelming the experience. It's up to you though - if you want it to cause your rig to dance across the room then go nuts
As far as I can see the controller sensitivity has zero effect on the wheel.
TL;DR
G923 Recommended Settings
Max Torque - 10
FFB Sensitivity - 1 (increase to 4/5 for road cars)
Vibration - 50