What can you tell from the numbers?
Phil, I have both an observation and suggestion I''d like to pass along.
First, the observation: As happens in many threads on boat design and boat selection on BBs like this one, I notice we have quickly moved from a general question about a few design measurements for a given boat to its suitability for sailing offshore and now to its keel depth vs. likelihood of capsize. IOW we''re now w-a-y over in one little corner of the general topic of the seakeeping qualities of a boat, which in turn is only one subset of your original question about its sailing qualities.
This is normal because I suppose we''d all feel irresponsible if we chose a boat that had inherently unsafe behavior offshore in a storm...even tho'' 99+% of boats never experience a storm, offshore. Not even once in their many years of use. And I would agree with Jeff''s conclusion: it''s a fool''s errand to attempt to correlate a specific draft with a boat''s inherent ability to avoid a capsize. In fact, I would argue a different perspective altogether: If we''re going to sit over in this one little corner of a boat''s mission - avoiding a capsize in a storm - then I''d suggest the main variable by a wide margin is how the ship is managed by the crew, which in turn should in part be a function of the crew coming to learn about the boat''s behavior and adjusting their practices and gear choices so as to look after the ship despite its vices, whatever they may be.
Which leads me to the suggestion: Given what seems to be your interest, I''d suggest you see if you can locate a copy of VanDorn''s Oceanography & Seamanship. There are two unique qualities of this book that make it a great resource: First, the book is in two separate sections, one discussing how an ocean functions on the surface and therefore how it affects a ship, while the second section then applies this theory when discussing seamanship in its various forms, including storm tactics. The second quality is that VanDorn is (or at least was) both a Professor of Oceanography at UC San Diego AND a seasoned seaman, on a wide range of vessels from sailboats to ocean research vessels...so you get a good blend of the theoretical with the real-world. You might find it very helpful not only in selecting a boat, but then in preparing her for the kind of ultimate conditions about which you are inquiring.
Good luck on the research!