The 2012 ARC results are posted
Overall, it was a good, fast passage. Finish times ranged from 14 to 17 days for the cats which didn't have problems or divert, which isn't bad at all for the course length of 2860 miles. That's 170 to almost 200 miles/day AVERAGE.
The Catana 43 finished behind the first Lagoon 560, and reported motoring 14.5 hours vs 12 for the Lagoon. It would be interesting to know the handicap basis for the cats, as the Catana had about the same rating as a Lagoon 450...
Comparing the times to the cruising monohulls is a bit trickier, but the 50th percentile cat had about the same corrected time (18.5 days) as the 50th percentile mono, which means the handicap system worked pretty well. Based on the assigned handicaps, the Catana corrected out first place in the multi's and 11th place in the monos, which is in the top 6% overall.
The boats in the ARC are generally more fully crewed and pushed harder than the average cruising boat. I would estimate that you should reduce the average speeds by about 10% for similar boats which are doublehanded by a cruising couple. The rally is almost all downwind in the trades--you could more than double the passage times if they went the other direction.