Clive,
I have AVO springs on the front now as you may know (or not) and I ordered the helper springs seperately. Those are way less then 50 lbs. I think more like 10-15 lbs and only help to do what you described firstly: retain the main spring onto the top perch at sudden full rebound.
I would have liked them a little more stiff than that, but its all they have in eitehr 2 or 4" length.. I guess AVO knows what is best, so I don;t worry about it too much
Walter