Keep the dongle, you can use it as a jig.
We don't know what the future might bring, a jig may be very handy in the future, i'm not sure what we could do with it in the future, but that's the point. I'm sure $ony has more uses for it than downgrading, right?
STOP! Before you ask questions... READ the first post! RTFFP = Read The F*cking First Post
Yes, A 3.55 "jb" (cfw) is available, no >3.55 "jb" or cfw yet.
Yes, A 3.55 downgrade is available. But not to lower than stock firmware! (What it came with)
No >3.55 downgrade is out there yet.