I'm surprised no one has responded to you yet. Though I am not so well qualified to talk about off shore passage making I am willing to share my impressions of Cape Dory yachts. First of all, they are classic beauties. Their lines and the way they are executed with lots of bronze hardware just say "sailing yacht". Also, classic full keel boats are said to be all around good, comfortable cruisers and passage makers.
Their relatively short waterlines and narrow beams do not produce much volume to support long term cruising. But spartan people like spartan boats.
Their shorter waterline also means reduced speed or longer passages, which can become problematic when trying to find a weather window to make a hazardous passage such as crossing the gulf stream.
Manuevering in close quarters like a marina can also be very difficult with a full keel, attached rudder boat.
The 33 would appear to be the better choice as it has a really nice nav station, and a good quarter berth for off shore passages. Yet the 31 has a newer interior layout with an aft head and very efficient looking galley. (But no sea berth).
A couple sailing a CD 36 ketch/cutter were in our marina a couple of years ago and I had a nice long conversation with him about how he liked his CD. Bottom line, he was very pleased with his boat, liked that he could work on all his systems without having to take it apart and could set quite a variety of sails, depending on wind and sea conditions.
Hope this helps.
ps. Read this Full or fin keel?
thread for insight on fin vs full keels.