Actually, with respect to downgrading, I was thinking more in terms of hardware. New hardware *should* be faster and more responsive than old hardware, but my Rezound, while pretty, is beset by delays throughout. That's the main reason I was hoping we would get Jelly Bean: it's supposedly been optimized for speed and responsiveness.
In the short term, I've installed GO Contacts EX, which does not suffer from the lag the native Contacts app does.