I owned a C320 for 12 years before moving up to the C355. I have to say that we loved the 320 and it is definitely not the day sailor of the bunch. For a couple, it is an ideal boat to spend extended time on in this size range. I agree with JK that the forward berth is cramped for two and that is really the only downside. The aft cabin is huge , so we learned to sleep there even though it is less than ideal. The forward cabin and shower arrangement were big factors for us in moving up to the 355. The 320 has more tankage, storage, bigger head and a bigger cockpit than the other Catalina's mentioned (and two sinks
As far as sailing performance, the 320 sails great. If you get a fin, she points high, can take a blow and is very forgiving. When over canvassed upwind she will round up as opposed to burying the rail. Off the wind is probably the best point Of sail due to her wide stern. Many 320s are actively raced very successfully. Engine access on the 320 is actually excellent. There is basically 360 access by removing cowlings both fore and aft.
What we didn't like about the 320 was the aforementioned sleeping arrangement, less than ideal shower arrangement, and the high freeboard. We were drawn to the lower freeboard on the 5 series boats. Gerry put these boats on a diet going back to the more traditional dimensions of the 34 and 36.