I would completely agree with Absolute0. The speed binning process that AMD uses actually can lean towards making the 'lower' binned products the faster clockers. Do a little research & note how the Athlon XP 2500+, and 2800+ would routinely OC far past what a 3200+, their top of the line would clock to.
If you absolutely MUST have one of the two, go with the Opty 180, as it's far more strenuously tested, and will, in all probability, clock higher than a 4800+.
As far as all that goes.... if you're willing and determined to shell out that much for a processor, get the FX60 & be a happy camper.