I'm surprised no one has mentioned this so I will.... The stock rockers although fool proof are rated at 1.5, but that's there not there true rocker ratio. I think there closer too 1.42-1.45 so there all over the place. Your not getting the lift that you think you are. You will see a improvement with a trued ratio alone, anything extra on top of that is a bonus.

If your head moves more air at the higher lift, then the 1.6 would really help because its also moving more air under the curve as well. This is provided you have the clearances too take advantage.