6.5 X 55,
I dont know if you like the design or not but I have made some Mollegabets at 72" that had very long draw lengths. I did not measure the exact draw but brought it behind my head (usually a 28" draw) so it was at least 32" The bow pulled that far with no problem at all. Another thing about the design is it will pull smoothly untill it breaks if you want to. The thin levers and "half" limbs allow the bow to come back a long way with little actual limb movement. [these bows were 48# and 50# at 28"]
I also made a couple of Prymid bows at 68" that seemed to pull a long way. Also some of my 50" size will draw to 29 inches very easily. So I dont think you should have any problem with your project.
One other thing is, my bows are all vertical grain and unbacked so if you back your stave style you should be ok. For what it's worth, I find my tight grained hard maple very robust and good, honest, bow-wood with good durability and very reasonable speed.
By the way....6.5 X 55 Sweed is a VERY sweet deer cartridge!!!!
half eye