I see a lot of Catalina 27s racing on the Chesapeake Bay. I believe they are all standard rig, as opposed to tall rig C27s, and all outboard-powered. Thus, all the tall rig 27s and inboard powered 27s are not good choices for racing. I think the boat is often owned by newer sailors who tend to be more cruising-oriented than racing oriented. As a result, most C27s have accumulations of old antifouling paint, and would not be good racers unless given a thorough bottom-stripping job. But, that having been said, large numbers of them have been built and are available, they can be bought without a big investment, they sail well, sails aren't so big as to be prohibitively expensive, and they make a good, fun, competitive, inexpensive racer that can also be cruised.
However, if I was going to race PHRF, rather than one-design, I'd race a Catalina 25 (probably a tall rig in the lightish winds of the Chesapeake Bay). It has a longer waterline than the C27, is lighter in weight, and is faster than the C27, but the last time I looked, the C27 had to give the C25 handicap time under most rating systems. In my opinion, the Catalina 25 (not the Capri 25) is an underrated boat for the very reason that so few of them are well-prepped and seriously raced, and they get a favorable rating as a result.
You can find tips on racing a C25 at Catalina - Capri - 25s International Association
, including suggestions on tuning the rig. Most of it would be equally applicable to the C27.