I think those numbers probably refer to the wall thickness of the tubing, in thousandths of an inch. Very few players get preoccupied with wall thickness other than whatever is standard, and it actually probably has very little bearing on tone. Best to stick to whatever is standard. I don`t think wall thickness is even mentioned in the Yamaha website on headjoint types....
http://www.yamaha.co.jp/english/product/winds/
Click on "woodwinds", then "Flutes", then any flute series 500 or higher, then "Headjoints".
The current most popular Yamaha head seems to be the "EC".
You need to TRY different heads, and YOU choose what suits you. People may suggest what works for them, but using words to describe tone quality is a poor means of communication.
my personal suggestion to try would be the head that comes with the cheaper Muramatsus. Others here are impressed with Powell heads. James
Galway was at least until recently, using a La Fin, and so it goes on.
Remember that a recommendation from a person who has possibly tried very few heads, should be taken as almost meaningless.... A person may really like their Lark head (Yuck!!!)until they become conscious of something better.