I've got a 3" or 4" Silverback and am not very pleased with it. Its about 5 years old so they may have changed their construction but the foam is very soft and not attached to the outside. This causes the pad to be like a balloon with some soft foam rubber in it. If its inflated enough to keep my hip off the ground, the rest of the pad bulges up around me and isn't very comfortable. If I've got just enough air in it to keep from having big puffy bulges, its barely enough to be soft and keep me off the ground. This may not be a problem for someone that sleeps on their back but I'm a side sleeper.
That said, the leafield valve is fantastic and i just wish more sleeping pad makers used a high volume valve. When I'm trying to break camp and get on the river the last thing I want is to spend what seems like foooooreeeeeevvvvvver deflating my pad and rolling it up. And that's with a 2" Paco Pad - I can't imagine how long it must take to deflate a 4" Paco pad through that dinky little valve...
if you're in Denver, give me a shout and I'll loan my Silverback to you for a test drive. If you like it I'll sell it cheap.