ARP often use a lower torque value than stock because the thread is finer (which still means it can actualy have a higher clamp load)

Think of a con rod and how the big end cap bolts to the rod, the more clamping force you give it the more out of round the circle will become and thus you need to then resize the rod. What I said is the A-series rods are quite resiliant to going out of round when adding a little extra clamp load by using ARP (some rods can go way out of spec)