I wouldnt worry too much about the centerboard on the Tartan 27. The centerboard doesnt provide much in the way of ballast so even if it fell off it wouldnt affect you too much. And since its so light it doesnt take much to lift and lower it. You shouldnt have the same issues that most trailer sailors worry about when it comes to a swing keel.
You might double check what I just said though. I have sailed with a friend several times that has a tartan 27 but have never had first hand ownership experience with it. There might be a whole more to it that I dont know.
All that being said if I was buying I would look harder at the other boats you mentioned.