Nigel,
My personal opinion is that most big (40 plus) calibres are very accurate in their own right, most of them, if not all, are capable of shooting better than the "nut behind the bolt". I believe calibres get more contankerous (sp?) the faster they get, rifles around the 2000-3000 fps mark just seem to be easier to get to shoot.

Just my thoughts though FWIW.

David.