Hi Simon,
I run OME 755 springs in the rear (280lb/in spring rate I think) and a pair of polyairs. I compromised when it came to respringing the truck and went from 330lb/in spring rate down to 280lb/in rather than go softer still. The polyairs get a lot of use. I have repaired one of them once using polyurethane glue that i use to patch my neoprene fishing waders... :D It has worked well.
I use the polyairs two ways - first is the obvious, lift when loaded (12-22psi); second is to dampen movement when on the road at speed (5-12psi). The higher pressure gives lift and the lower pressure causes the springs to sway less much the same as a swaybar would I guess. Seems to work out OK. If I am wanting full and free articulation (who doesn't :)), I get a broom handle and push air out of them so as they are shrunken inside the springs and not able to cause articulation dampening...
You need to be able to do this...
https://www.aulro.com/afvb/images/im...10/12/1024.jpg
https://www.aulro.com/afvb/images/im...10/12/1025.jpg
without this happening..
https://www.aulro.com/afvb/images/im...10/12/1026.jpg
Phil