iH8sn0w, a well known hacker who developed the jailbreak solution called “sn0wbreeze” & “iFaith” has found a way to downgrade the Firmware on A5 devices (iPad and iPhone 4S).
He achieved this via saved SHSH blobs, in his twitter post he said that he was able to downgrade his A5 iPad 2 from iOS 5.1 to iOS 5.0.1. He also makes it clear that the method he used will also work on the A5X processor (on the new iPad) once the firmware updates are released for the new iPad.
It looks like you could downgrade to any iOS as long as you have the SHSH blobs saved via Cydia or TinyUmbrella.
