Don't go lower in spine. The ones you shot are too weak. If you get a shaft that is way under, it will hit left with feathers on it. What happens is the excessive shaft flex pulls the tail out way left on release, then the feathers straighten it out causing a hit to the left. You can bet if you shot one of those 55/60's bareshaft, it would leave the bow nearly sideways nock left.
At 29.5 bop from a center shot bow, I think I would start with at least a 65/70, although a 70/75 would probably be better.