Udi,
The PRA recommendation of many years ago is about 0.8" of cyclic stick travel per degree of rotorhead movement (I forget the exact numbers - they used a slightly different number for pitch and roll).
Most experienced builders I've talked to say pitch and roll sensitivity of 0.75" per degree (measured at the top of the cyclic) is nice for beginner gyro pilots. Experienced pilots seem to like a bit more sensitivity down to the 0.6" per degree, but anything less than that starts to feel overly sensitive to most pilots.
Chuck Beaty has said on Norm's old conference that excessively insensitive control ratios are just as bad as an overly sensitive one!
Regards,
John L.