Dan, excellent questions. Unfortunately there is no easy answers, too many variables. You are right that roll center height is a big determining factor, on the front as well as the rear. Wheel rate, track width, tire size etc all play a role. What kind of car are you working on?
I am a believer in "softer" springs and stiffer anti-roll bars, some folks think just the opposite. It is really up to you. If it is an unusual application, an adjustable bar would be desirable. If you could give us some more information on your car we should be able to steer you in the right direction.