I've been shooting CX 150 Heritage arrows in 50lb and below bows with no issue. When I try the CX 150's in my bows over say 53lbs, I get a whip with any tip weight over 125grs. With 125's it flies pretty good. With 150grs, it fishtails.
My arrow is 32 1/4" from the end of the nock to the end of the insert.
My arrow weight with a 125gr tip is 520gr's.
If I wanted to expand my broadhead options or get up to 600 some grains, if I was to go to a CX 250, where should I start on bare shafting? Should I try a 32" in a CX 250, with a 54-58lb bow? I'd like to shoot 150gr Stingers, since I have a bunch. But with the CX 150's, 150gr heads do not fly straight. Any thoughts on what length a CX 250 should be, to shoot 150gr heads?
Thanks in advance.

If it helps, I shoot a 30" 250 from 56lb recurve with ff. Standard insert with 165 grain point. Shoots Woodsmans great. 565 grains.  Best bet is to pick up a single shaft or two, start full length, and trim down until you bareshaft like you want. I found mine to be fairly sensitive - half an inch makes a difference when you're at about the right length. Good luck.

Shoot a bare shaft!  They play with the tip weight to get to the length you want.  That is the easiest eay to figure out your spine.  Once you get that to fly right then any fistailing is due to other factors, like contact with the bow shelf or your release.