For what it's worth, I was in almost exactly the same position 18 months ago as it sounds like Shawn was when he bought -- was looking to purchase and drawn strongly to both the B35.5 and the T37. We ended up going with the latter and, after our first year of ownership and use, we couldn't be happier with our decision.
On the issue of cored hulls, Shawn's comment is spot on: there's ample discussion on the subject and you'll sort of just have to decide where you fall on the whole issue. Us, we weren't terribly fazed by the prosepctive drawbacks of a cored hull.
If you haven't read Jack Horner's reviews on both, I suggest doing so. One of the most helpful comments I ever heard about the B35.5 is how tightly packed in everything is. Engine access in particular is a pain on the B35.5, whereas I've been extremly pleased with how easily I can get at the fuel filter, raw water strainer, impeller, and the likes for my T37's Westerbeke. Additionally, while the difference in length is <2 ft. between the two, I feel like we get a lot more elbow room on our T37 than on the B35.5.
There are those who will argue that Tartan's pedigree or prestige is a notch below Bristol's. I'm sure many would say that's a debatable point, but it's probably a fair argument. Still, I think Tartan 37 is a boat of unquestionably good heritage and, as a liveaboard, I think some of the advantages it presents (esp. regarding space) could be extremely appealing to you. All the best in your search. . .that is, if it hasn't concluded already (I've been off SailNet for a little too long)!
Tartan 37 Hull #228
Harwich Port, MA