Please consider that as far as I know the sensitivity setting does not really change the sensitivity but the progression of the break signal from your controller.
For a "normal" (with normal I mean
no load cell) break pedal this means that no matter what you set there, if you push the pedal 100% to the end you will have 100% break pressure but the progression to 100% changes. As far as I know setting the sensitivity to 50% means having a fully linear progression - you push the break pedal 20% down, you will have 20% breake pressure, 40% break pedal position means 40% break presssure and so on till 100%.
Changing this setting higher than 50% means that you will have a progression that rises more at the beginning, but less in the end. Lower than 50% means the opposite - less progression at the beginning, more at the end.
At least this is my knowledge - if anybody knows better feel free to correct me.
I don't know how load cell pedal drivers convert the load cell signals to input signals, but it has to be somewhat different since a load cell has no fixed limit. I don't own a load cell break myself, but taking the above into consideration and thinking that a load cell break should somehow simulate a real break pedal in itself, I think that for load cell breaks a setting of 50% sensitivity should be fine.
For my T500 RS with the so called "realistic break mod" a setting of 0% sensitivity has proven to be fine for me. It comes quite close to the behaviour of a real break.
Considering the characeristic of a real break a low sensitivity setting seems the most realistic for non load cell breaks - but in the end it also depends on what everybody likes and/or is used to.
Just my 2 cents.
Cheers...