The Cape Dory 28's are nice little boats. I actually like the Cape Dory 28 more than most of all of the Cape Dory line. For their day they were wholesome designs with a reasonable amount of waterline length and a nicely modeled underbody.
To me they are complex boats to classsify in a lot of ways.
I don't think of them as good daysailers or good boats to learn to sail on. I think that ideal daysailors and boats to learn to sail on are responsive so that you can feel the full richness of the sailing experience, the subtle clues to the impact of wind and water or response to small sail trim or steering changes.
I don't think of them as being very good coastal cruisers. Their excessively high weight and small sail plan do not make them very handy in the changeable conditions and lighter air typical in coastal cruising. I think that this is a personal preference thing, but I think that coastal cruisers need to accel in a wider range of conditions, and offer good enough performance to run for cover or beat off of the more frequent hazzards found inshore. In my mind, on that basis boats like the Cape Dory 28 fail my sense of a what a good coastal cruiser should be.
By the same token, my opinion of them is complex when I think about them as offshore cruisers. These are good boats in a lot of ways for offshore use. If you start out saying that you want to go offshore in a 28 footer, these boats have reasonably good tankage and a reasonably good layout for a boat that size, but small for any serious cruising. If I remember the interior correctly, it would be pretty easy to adapt the main cabin settees to good seaberth. It would take some pretty serious alterations to the interior to install more than a single burner gimballed stove or a proper navigation area. Most have an engine that is way too small for a Cape Dory that is fully loaded for cruising. But the price of the large tankage is that most of the other storage is quite high above the waterline.
While I would hate to re-ignite the discussion of the definition of a fin keel vs Full keel, which has taken place on this site many times before, I would like to touch on the comment that the Cape Dory 28 is a "full keel" boat. It is not. As I have pointed out, that the past, histroically the defintion of a fin keel was a "A keel whose length on it bottom is 50% or less of the LOA or length of sail plan which ever is longer". By that definition the Cape Dory 28 would be a fin keeled boat with an attached rudder.
As has been pointed out in prior discussions, this definition has dropped out of popular use, and to most people who have started sailing in recent decades, these boat are not fin keelers. I think that the general consensus was that boats like these were moderately long length keels. Whatever you call them, they certainly are not Full Keeled boats (I suggest that you look at the Bristol Channel Cutter or the Westsail 32 if you wish to see what a full keel actually looks like.)
In any event, whatever you call the keel on the Cape Dory 28, they have a sharply cut away forefoot, and a rudder post that is quite far forward in the boat, and an attached rudder. This results in boat that does not tarck all that well and which can develop quite a weather helm. What is nice about the Cape Dory is that you can reduce sail area and help balance the helm. But that occurs at windspeeds that would further slow the Cape Dory below newer offshore cruisers (Take a look at the Southern Cross for example) or boats with hulls and rigs that can benefit from better sail handling gear.
This brings us back to your original question. In waves large enough to roll a boat, it is generally thought that a limit of positive stability as loaded in the range of 125 degrees should be adequate. Which is not to say that there this is the only LPS that you see recommended. I have seen recommendations as high as 145 degrees, but these high limits of positive stability generally refer to LPS based on a 'dry' loading. In big boats there is comparatively little difference between an LPS based on the dry loading vs fully loaded. But in smaller boats, like most of us around here seem to sail, the vertical center of gravity rises pretty sharply when the boat is fully loaded for offshore cruising. This is especially true boats like the Cape Dory where a lot of the bulk storage is above the waterline.
If I had to guess, based on stability plots that I have seen for similar boats, I would expect the Cape Dory to have a limity of positive stability somewhere in the 120 degree range. In the CD 28's favor when it comes to LPS is a reasonablely deep draft, and high freeboard and cabin structure for a 28 footer. The ballast to weight ratio is also reasonably good for a boat of this era but would be be absolutely dismal when fully loaded for offshore use. Another negative re LPS is the Cape Dory 28's rig which is very heavy for a 28 footer and while pretty sturdy, makes a good ballast keel when inverted.
The other component of inverted stability is how stable they are inverted and the CD 28 is quite beamy and the beam is carried quite far towards the ends of the boat giving the boat a bit more inverted form stability than one might expect. This is partially offset by the large volume of the cabin structure.