which 38ft boat?
I believe that you are mistaken that the Island Packet and the Hans Christians have better inherent stability in heavy air when trimmed properly. Both of these boats have a lot of form stability that comes from their wide beam, a lot of weight for their length, and a comparatively small sail area relative to thier displacement. That gives the illustion of a lot of stability, but does not result in a lot of actual stability. Both of these boats exhibit a lot of drag relative to their stability, and as such need to carry a lot more sail area in heavy going than a more easily driven hull form and at that point their relatively low stability in relation to the amount of sail that needs to carried to overcome their drag,means a comparatively higher heel angle and helm loads. Neither are especially good heavy air designs relative to more modern offshore oriented designs.
Island Packet had a achieved a relatively high angle of positive stability by raising the height of their freeboard and increasing the cabin volumes on their boats. This comes at the price of carrying a their weight much higher than ideal and results in a fairly high VCG (vertical center of gravity). A high vertical center of gravity reduces stability and increases the tendancy to roll quicker (somewhat offset by the boat''s comapratively high inertia) and through a wider roll angle(somewhat aggrevated by the boat''s comapratively high inertia). The Hans Christians with their heavy decks and interiors also have very high vertical centers of gravity and have a significantly lower ballast ratio, but also lack the higher freeboard that Island Packet uses to increase their limit of positive stability. With their wide beams both of these boats require a lot of energy to re-right once overturned.
One other point, in your post you say "the IP and HC have somewhat better inherent stability in heavy air when trimmed properly." My experience with IP''s is that they have really poor deck hardware making proper trim very difficult or imposible in heavier going. This problem is even worse on the inmast furling boats where luff tension cannot be controled with the mainsail partially furled. I know that IP uses a lot of name brand hardware, but the deck layouts are such that controlling twist in the main or making changes in jib sheet lead are extremely diffiicult and the problem is only exacerbated by the use of comparatively high friction Ronstan solid sheave blocks and mid boom sheeting. Most quality builders have long since gone over to the more expensive, longer lived, and lower friction roller and ball bearing blocks.
With regards to the Hans Christain, a 1987 model is 17 years old and is likely to need a major overhaul and update if it is going to be doing a lot of offshore work. I also would discourage you from buying a HC that still has its teak decks. That should be a deal killer on any boat intended for offshore long distance cruising.
On the other hand, a boat like the Tartan, while it has a lot of stability relative to its drag, also has a more generous sail plan and so might need to be reefed sooner as the wind builds than the other two boats. That means better lighter air sailing ability, less motoring but a little more work. If your nom''d net ''bluewaterdreamer'' means anything then I would suggest that the Tartan, while it is a really nice boat, is really more of a coastal cruiser than an offshore cruiser lacking the kinds of seaberths and large bulk stroage located low and central in the boat that is so important for distance offshore cruising.
I guess at the heart of this discussion is the question, where do you sail and where do you intend to sail. If your plan is to stay coastal for a while then perhaps the Tartan is a good boat. If your plan is a mixture of coastal and offshore, then perhaps you should keep looking.