Spine and weight for bamboo arrows shot off a thumb ring

I shoot a 42' (@31") composite Turkish-style bow with a thumb ring. (If you don't know about the different dynamics of thumb release, this question's not for you.)

I make my own arrows and I'm looking to get some decent bamboo shafts and make up some arrows. The informed sources about Asiatic archery and bamboo arrows say that (because of bamboo's different resonant frequency/ something else; no-one really seems to know why) you want to choose arrows of about 20lb higher spine for bamboo...

Spine and weight for bamboo arrows shot off a thumb ring