I've been meaning to give Fir a try. I think Steve (Badger) said he had made Fir bows when he was working on his mass theory. If it back make-up most of the depth of a bow with a thin bit of Hickory on the back and a bit of Ipe on the belly it should make for a very fast combination, sort of like a modern foam-core limb.
Updates on the warbow in about an hour, glue cured rock hard in less than 36hours outside. Using the innertube method I have perfect glue-lines this time, no more clamps for me I've learned my lesson.
Cheers,
Grant
Edit:
This is the stuff: