Upload & Sell: On
Learn the options well and you'll learn to love it. The lens will focus much faster using the lens buttons over calling focus via the body. I disable shutter focus and I don't recall ever needing to hit focus on the body when using memory recall, it just pops into focus and I shoot.
Just set up in one place (not like the 600 is a walk around lens anyhow), memory lock it on a place where there's lots of action and shoot normally for the balance of your field of view. Then when a subject hits that spot just swing over there and press the lens button once while doing it and you'll be in focus by the time you get on subject. Yeah, even if you're almost on the subject. It's that fast.
AF-ON is handy when you are just searching around for subjects and want to focus on them fast. I only use it when walking with my 500 as my hand is there. I found it too far out there on the 600 when swinging around on the gimbal, but that's just me. I sure miss the 600, but love being able to walk n shoot with the 500