Roller lifters are heavier and won't rev as high as no-roller's before the spring can no longer control the lifter.(float)
Yes, the ratio you describe is correct. Roller rockers also allow more movement on the vertical plane and better alignment of the valve seat face with the valve head creating a better seal to trap combustion pressure. A non- roller has a tendency to push the valve stem out of position increasing wear on the giudes at higher than stock lift's.
Stiffer springs can control the oscillations of the entire valve trian by reacting faster to cam. They won't lose controll as soon.
RPM ranges are just intendes to give us an idea of what to expect based on 350 engine's. More cubes will make a small cam act different then if that same cam were to be used in a small cube engine.