From what I recall from the intro of the Duron- at 700 it was roughly equal to a Celeron @ 850. From Anands review:
"A Celeron 566 overclocked to 850MHz (100MHz FSB) begins to restore competition to the value market as it can begin to measure up to the performance of the lower clocked Duron 700. At the beginning of the year Intel told us that they didn't move the Celeron to a 100MHz FSB because there was no reason to, well AMD just gave Intel 5 letters that spell out exactly why the Celeron needs a 100MHz FSB. Don't be surprised if you do see a 100MHz FSB Celeron in the future (not in the near future though), we already know that the Celeron can run on a 100MHz FSB, it's just up to Intel to decide when they should make the move. Even if Intel is to introduce a Celeron that runs off of a 100MHz FSB, clock for clock, as we have already proven, the Duron is the faster part."
I assume the 600 would be roughly equal to a Celeron @700-750.