Andreas I can't help you directly, but I have ordered a 72# caribow and have done some similar research. If you go by the spine calculators they suggest a .200 spine shaft for my setup, to end up with 10gr/lb and about 350gr up front. However a lot of guys on this forum shooting bows in that weight range thought I was nuts going that stiff, they are using 300-350's,with up to 450gr up front.
So I would suggest it is well worth a try going with the 300 shafts. Black Eagle make some awesome options.
Let us know what worked out for you.