Which Island Packet?
A couple minor points just to keep this discussion ballanced, first of all not all fin keels are bolted on, so full keel or fin, you would not need to worry about keel bolt failures with an encapsulted keel. That said, you do need to worry about the much more common encapsulated membrane failure, and ballast to keel membrane failures. In general amoungst respected yacht designers, encapsulated keels are considered a cost savings measure that hurts the seaworthiness, longevity, and sailing ability of the boat.
I also need to ask Danny to explain why he seems to be more worried about keel bolt failures than he is about having a post hung spade rudder that is virtually the same depth as the keel. Generally accepted good design practice, expecially on a shallow draft boat and especially with a post hung spader rudder is to keep the draft of the rudder well above the depth of the keel to protect it from damage something that Island Packet has chosen not to do.
Full keels add nothing at all to the seaworthiness of a vessel. In fact, within the design community the greater drag of a full keel is seen as a liability when it comes to seaworthiness since it means that you need to carry greater sail area in heavier going to over come that increased drag. All of the more recent studies that I have read and attended design symposium on, point towards a set of desirable characteristics for an offshore boat that would include a comparatively narrow(within moderation) easily driven hull forms, with comparatively low drag foils (within moderation), comparatively low freeboard, comparatively small deck areas, and a comparatively high vertical center of buoyancy coupled with a low vertical center of gravity. In other words, pretty much the opposite of the design thinking behind an Island Packet.
"This boat shows it''s true colors off the wind." I agree with that except that Island Packets sail their best in a narrow range of wind speeds when reaching. They are miserable dead downwind and upwind. They do not do well in heavy going compared to more moderate designs with lower center of gravities, and they are useless as sail boats in light to moderate conditions. Distance cruising means being able to sail where you want to in a wide range of conditions. The alternative is either carrying a lot of fuel or not being able to go where you plan to go when the conditions don''t cooperate. While no one would want to be beating "in the Gulfstream when the elephants are marching" (or motoring into the Gulfstream "when the elephants are marching" for that matter), there are a lot of times when beating or close reaching is the only way to get somewhere other than aground or motoring.
While you may have met someone somewhere who put down Island Packets because "It''s too much of a good thing", most of us put them down because they sail poorly, and are poorly detailed.
All of that said, if for some reason the original poster still thinks that they need to buy an Island Packet rather than a boat designed to be a true offshore cruiser, I would agree with the suggestion regarding the 380, because the 3''10" draft on the 40 footer would take an already poor sailing boat and hurt its sailing ability further. I do think that the use of lead ballast is a major improvement over the iron in concrete ballast of early models.