To guage the perfect length for me, i hold the gun in one hand, then turn my hand palm up so the bottle is resting on my forearm, if the back of the bottle reaches the joint in my arm its the perfect length.
That's a fair point and is generally true but in my case and others that simply doesn't work. It's not like i'm an Ooompaloompa or even a plain old Midget but the bottle is always to far past my joint.
I'm using a CP rail and Oops and a PMI preset but i still have to push the Oops as far forward as it will possibly go just to stand a chance of manouvering behind the gun.
I switched away from a drop because fashion and ridicule dictated i should do so, but although i'm now used to my current set up the drop was easier to play.
Also people keep banging on about that height rubbish, unless your playing like a numpty, you sight the gun at eye level like usual and position the bottle lower into your body, doesn't add any extra height at all.