Would it be safe to say that a Cat 22 would be more stable than the O'Day? I don't believe it has the centerboard.
If by "stable" you mean "less likely to capsize", then no, I don't think that is the case. The centerboard on the Catalina doesn't give the boat more stability than the stub keel on the Oday. The centerboard is primarily a more efficient foil than the stub keel, allowing the Catalina to sail closer to the wind. If by "stable" you mean will the Catalina heel less, then that may be true, but only marginally.
With boats of this size and age, I would go with the boat that has the most solid deck and hull, the best sails and the best outboard. Those are the three items that are (from highest to lowest) the most difficult/expensive to fix or replace.
One other feature that recommends the Oday over the Catalina: the head in the Oday is behind a bulkhead with a door. Never underestimate the value of this feature when sailing with the ladies. By contrast, the head in the Catalina is out in the cabin. If you want privacy, you have to chase everyone else out from below and close up the hatchboards. A real pain.