not so easy
It is hard to make direct comparisons as the design briefs were so different and from different eras..
The 27's fuller underbody, while considered a fin keel when introduced, was shallow, thick, and very low aspect compared to the keel types seen on the 25+/26, 28+/28 and the 30+. For the waterline, the 27 has quite a bit more wetted surface area, and quite a bit more displacement (overall weight).
The result is she can carry more weight (or a higher percentage of her total weight) in people, gear and stores before suffering performance losses compared to the more modern types. As you surmised, the older design is arguably more comfortable (less "jumpy) in a seaway, although with a lower SA/Displ and SA/WL ratio, the 27 will also be slower when flying comparable sail combinations..The keel shape, aspect ratio and thickness of the 27, coupled with wider sheeting angles for the headsails, makes for a less "weatherly" boat than the newer series-which have relatively deeper, thinner keels, and more inboard sheeting positions-so it will not point as high.
This is not to say the 27 is a poor boat to windward, for its' time, it did very well..but the newer designs are better in this respect.
I would give very little weight to the issue of capsize ratio-both boats are certainly seaworthy when properly equipped and prepared. Both will come back after a big knockdown-as long as you keep the wet stuff (outside) away from the dry stuff (inside). This risk is largely due to large waves coming in over the stern, filling the "pit" and then the cabin. In rough weather, use a one piece hatchboard that is properly secured to the hatchway-we have reviewed this procedure several times in the last 2 years, so it is worth a closer look.
Being smallish boats, they are both very affected by weight and weight distribution, and both can improve base performance greatly by paying attention to these details (keep weight out of the ends as much as possible; do not become a floating hardware store or floating "Linens and Things".
Both were very good performing cruisers that have acquitted themselves fairly well racing (the 27 in fact has the better race record, but is treated very well by PHRF, whereas the 25+ looks maybe a bit faster than it really is, and the rating reflects this.
I think the newer boats have more inside volume (which temps owners into being mini-frieghters, which does not help), and thus they are somewhat better for on board entertaining.
A very good practice for either is to carry on board those truly essential things you would want on every outing, and leave most of the specialty or trip specific pieces of gear in the dock box-bring it when you need it..either boat will be more lively this way and perform much better.
Also for performance comparisons, make sure both bottoms are in good shape, props are similar and shafts are marked (when applicable), and fly decent sails with genoas of about the same LP..
There were advances in construction and engineering between the 27 and later boats, with the 25 benefitting from this with a lighter, stronger structure, but this does not mean the 27 is poorly built-on the contraary..
Both are very good values and the main thing is to keep in mind you are making an apples to oranges comparison, rather than apples to apples..
If both attract you, compare the overall condition, including bottom and mast, equipment-including deck hardware upgrades, blocks, engine condition and sails,and then the price. If you make a weighted features table, one of them will emerge as better for you.
Both will get you there is style and good speed for the size.
Happy Hunting,
S
