Martin Carthy appears to use cgcdgd,cgcdga,for tune playing
MARTIN states in his book that dadeae enabled him to play in two keys d and a, he then dropped the tuning a whole tone to suit his voice he goes on to say that later on he dropped the top d down to a and ... by using cgcdga, he could play in four of five keys c.g.f.d. and possibly a minor.
he also says he used dadgad for sailors life and although he liked the sound he found it confining and never felt comfortable using it as he could only play in the key of d.
of course this is only Martins opinion, but his comment about more flexibilty of keys in cgcgda while retaining the open key sound is very interesting.