3 rivers has a spine chart for carbons as a pdf file from the carbon arrows catalog page.It shows 55-75 for my 52#@29.5 with 30" arrow 125 gt tip.I am presently shootin 400spine easton epics with a 125 point and they seem fine.a little light at 450 gr but some weight tubes will fix that.I used to use some black tubing from hardware store @9.1 gr/in in GT55-75s but think I'll get some carbon express tubes made for the purpose.
Short answer:55-75 seems good from my longhorn at 31"length,I also have tried 100 gr brass insert with the 125 but that is too weak,I think the 75-95 will be stiff @28.5" for you. Try a bareshaft with the 2 fleched and let us know .Hope this helps.