You can get the book answer on slowness here;
PHRF New England - Handicapping - Base Handicaps
where you'll see the CD rates 207 versus a 174 for a C&C 30. Now 33 seconds a mile wont make a good day of sailing bad, for being a little slower. But these ratings are for average wind speeds, my experience is that in lighter air the slower boats completely stop a lot sooner. What that may mean in your venue is that with a C&C 30 you might enjoy Summer sailing sailing 70% of the time you wish to, whereas with CD 30 you could sail only 40% of the time you wish to.
So the slower boat means you get 40% less sailing. If you want to enjoy your Summer in a light air venue, get a good performance boat, and even then, equip her with a 150% genoa and a spinnaker (preferably an oversize furling asym on a 4-5 foot sprit), and spend a lot more of the summer, well, sailing.