I have a cutaway forfefoot keel and while they turn on a dime when the wind is just right, they are sluggish at low speed and I have had a few problem tacking when the wind was really strong just like I had on cape cod mercurys so it's not just the shape.
I approach my boat rationaly, it's a machine with nice features and flaws too. It's a little disconcerting to see people swear by the design they happen to have (sometime by luck) and get into pissing contest about the shape of their keel. All this talk is nonsense, the only persons I would trust in this matter are boat designers and naval architects. Let them discuss the merits of such and such configuration. The rest is legend and fable.
Well, if you take it that way it is rather simple: Naval Architects, I mean reputable ones, have long abandoned full keel configuration even for blue water cruising purposes, even the ones that once, far in the past, designed full keel boats.