Most of us have our idea of 'too soft' vs 'too hard' vs 'really hard' based on experience with the machine. But if you are uncertain about that I think you can benefit by putting your Pavoni on a bathroom scale and playing around with pulling against a relatively choked shot. Might work better than thinking about knives and butter and cheese.
This has been discussed on HB, with the advice that around 40lbs is right*. This is in my opinion too hard. It also looks too hard when I do a simple calculation. By my calculation a 30 lb pull is about right for 9 bar brew pressure.
Here's my calculation:
Pavonis have 44mm gaskets, so the cylinder radius is about 2.2cm giving an area of:
9 bar = 90 N/cm**2 = 9.18 Kgf/cm**2
So the force at the piston is:
2.2 cm**2 * 3.14 = 15.2 cm**2
If you measure the distance between the fulcrum pin and piston rod pin (24mm), and measure the distance from the lever handle grip's end to the fulcrum pin(265mm) you will get a ratio of about 11/1, and a practical lever advantage of around 10/1 to the point an inch or so in on the handle, so ...
9.18 Kgf/cm**2 * 15.2 cm**2 = 140 Kgf
140Kgf/10 = 14 Kgf = 31 lbf at lever handle
When pulling 9 bar you are pulling with more than 31 lbf in a vector directed towards the machine's base (to keep it from tipping) but the downward vector measured by a bathroom scale would still be around 30 lbs.*It's amazing how often you hear the 40 lbs figure for pulling 9 bar. I think this comes from an old alt.coffee post - http://alt.coffee.narkive.com/LVokoYhH/...so-network. That figure was a guesstimate, and used a lever advantage of only 8:1. I like mine better because it's based on the actual piston seal diameter, and an actual measurement of the lever advantage.