I haven''t heard of anyone doing crossings, but I suppose it would be doable. My first boat was a Tartan 27 which I sailed in New England for a couple of seasons. It''s a good sailing, sturdy boat. A dock cleat broke loose once in early spring during a storm (I was out of the country at the time); while I had to have some work done to repair the bow she actually did much more damage to the dock than was done to her.
If you own a T-27 and you''ve never read "The Coast of Summer" by Anthony Bailey, you should do so. He doesn''t go offshore, but he takes his T-27, "Lochinvar" around New England for a summer of coastal cruising. Still and interesting read, and if you know the boat his descriptions feel...comfortable.
Also "My Old Man and the Sea" by David and Daniel Hayes is about taking a small (25 ft) boat around Cape Horn. Not a Tartan, but similar in stature.