I read up on the Barton core processors before buying a 2500+ (but they supllied a 3000+ by accident, oops). Lot of sites tried over clocking these processors but with not a great deal of success. The 3200+ particularly did not move much when ocd. A little but not a lot. I don't think these processors are particularly suited to overclocking.
Saying that that was 6 months ago and it is possible that newer mobos might have more success.
They all run quite hot so you'd need some serious cooling to oc a 2800+. The AMD boxed cooler can't cope with a stock 3000+ never mind an ocd processor.