Which Island Packet?
Remember that these are races that are scored on a handicap. In other words these boats may have finished days or even weeks behind the rest of the fleet and yet still corrected out to a good finish. That does not make them fast in absolute terms.
Beyond that, Island Packet''s ratings somewhat reflect the fact that they are not optimized for racing nor are they generally sailed as a racer would sail a boat when cruising. They tend to be delivered with sails that are not performance oriented and deck hardware that limits the ability to control sail shape. A few years back I read a piece about one of the IP''s that did well in the Carribean 1500. The owner of the boat, (a former racer) described what the fairly extensive changes that were done to optimize performance and with these ''unrated'' alterations he felt that the boat had a slight gift rating that would pay off when combined with being sailed as a racer (vs typical cruiser) might sail a boat. That said, he also noted that it was a lot harder to keep the Island Packet up to speed (they were quick to lose speed but hard to get it back) than it was with the race boats that he owned and raced in his prior life.