I've owned a Tartan 37 for 15 years so I will try to answer your concerns about the centreboard.
1. I don't know if anyone can answer your first question - centreboard vs. fixed keel version of the Tartan 37. You might want to go to the Tartan 37 website and ask that question. I assume that the fixed keel can point a little bit higher that the Tartan 37 CB down. I can tell you from my experience that in pointing, the centreboard down allows me to point approximately 5 degrees higher than with it up. Again, so much depends upon proper tuning, the shape of the sail and the skill of the crew. I race my boat, and am able to point very competitively with other boats in the cruising class; on a reach or
downwind, with the board up, they have a lot of trouble keeping up with me.
2. My centreboard has never rattled and I have been in serious weather over the years. A tartan hold it value.