Totally agree FLL. I had forgotten about the "Numbered" boats. In the old days, most ..if not all O'Days had
names...Like Daysailer, Mariner, Outlaw, Rhodes 19, etc. Until you woke up my memory, I had totally forgotten about the "numbered" boats in that size range that came later.
THE One that now comes to mind is the O'Day 22. I'm sorry I can't say anything complimentary about that boat....primarily its Sailing Characteristics. It was a keel centerboard like the 20. The 22 would NOT go Up Wind. At the time I had a Pearson Ensign (22') and the two boats were no match. The O'Day 22 may as well have been 15' because I could just walk away from it with the Ensign.
The Ensign was a full keel boat with inside ballast and 400# more weight, and might be expected to out-sail a lighter keel centerboarder on the wind...but not the great difference I found. After all, they were both 22'.
One thing I always took into consideration when I would run across a poorly performing boat was the skill level of the skipper. After all, the O'Day 22 WAS an entry level boat.

NB
EDIT:
http://sailboatdata.com/viewrecord.asp?class_id=79
EDIT:
http://sailboatdata.com/viewrecord.asp?class_id=162
PS: FLL: That's a handy little site. I'm saving it.