Lets just imagine that map in the mail is absolutely accurate. The aircraft seems equidistant from most eastern seaboard destinations. What with Gander/St Johns being the closest to the uk, it seems an eminently sensible place to go. Add to that the fact I have no idea of the TAFs for any of them, it hardly seems an unreasonable place to go for an immediate landing.
I've often flown a track similar to that from FL back to the uk. Wind is just as important as track miles over the pond.
With the extra track miles flown, 5 mins to arrest the man, 30 mins to gas up, 45 mins to get some paperwork/brief, and 30 mins faff time, 3 hrs sounds fair to me.