My current set-up is a Martin Hunter, 54@29, Fast Flight string, 30" GT 5575s with a 100 grain insert AND a 250 grain head, 3 5" feathers.  They shoot slightly stiff bare shaft.  I was thinking of trying wood arrows in the 60-65 or 65-70 spine range.  Does that sound OK or do you have another recommendation?

i think you may have to go to 70/75. I shoot 65/70 out of my 45lb curve,30 1/2" arrows at a 30" draw.I also uae 160 grain head.My bow is also 3/16 past center on the shelf.

A 55/75 is a 400 spine and that is equal to a 79lb. wood arrow spine.

You haven't told us your draw; but assuming it is 29, and the Martin is likely center cut you would be best off with 70-75 as was recommended by Steve.
Get a couple of different spines and bareshaft them. Most sellers will work with you and sell you a few shafts in two or three different spines..

And get one of cupcake's spine meters while you are at it. Mine works great-I use it almost daily, and a feast for your eyes.