Here's a simple way to figure out your length of pull. Bend your trigger finger at 90 degrees, and measure from the inside of your bent elbow, to the pad of your finger. That distance is your length of pull. Make sure you measure to the first joint, where the trigger would normally sit. My LOP is nearly 15" and I rarely need a stock cut. (of course my knuckles drag when I walk though!)
Hope this helps.