ORIGINAL: PABowhntr
I think buckfevr may have hit on the answer. It sounds like you found the best draw weight for the arrow that you are currently using. It makes perfect sense that as an arrow becomes more and more underspined then it would be less and less efficient. Though the arrow might still offer up good accuracy at 70 lbs I would be willing to bet that you could get better accuracy at the 62 lb draw weight.
Should've went with a "heavy 60 lb model"....:shakeshishead: [&o]
I'm with BF and Frank. Thats where the spine is optimum. the BT PF cams, especially the older designs like a STIFF arrow. I shot 3-49s out of my 29/70 2002 Pat, and they shot field points and mechs fine, but when I put fixed blades on, thats where the weakness in spine showed up. Had to bump up to 340 class shafts to get good flight.