I am a long time Predator shooter...
My draw length is 29 1/2 inches, and my draw weight at that length is 73 lbs.
I have ALWAYS found it necessary to shoot arrows spined heavier than any chart ever recommended from this bow.
When shooting wood shafts, I need nothing less than the heaviest spine I can find. 90 to 100 lbs spine for wood shafts...cut as short as I dare.
My son shoots a 50 lb Predator, and draws right at 28 inches. His best flying wood arrows are spined 60/65 lbs and are 29 inches long. Honestly it has been a while since I watched him shoot the wood shafts, but I think they show weak, and could stand to be as short as possible. His shafts are Cedar, and I believe they finish out at just shy of 500 grains with a 125 grain glue on point.