HaveVoid -
I suspect that your "experts" don't own or use either the 100-400 or the 400 5.6. Most likely, they don't use either of these lenses on a 7d. I own both lenses and a 7d and I can assure you that the 100-400 does indeed autofocus on the 7d and is a very sharp and capable lens. I use my 400 5.6 on a tripod and shoot birds and offer the same praises and capabilities as I did with the 100-400. I might add, that my 400 5.6 is probably a touch sharper than my 100-400. The 400 5.6 auto focuses faster than the 100-400 and the lack of IS on the 400 5.6 is a non issue for me since I use the lens with a tripod.
My AI Servo settings are the same as neuro CFnIII-1 - one above the slowest, CFnIII-2 - 0 and CFnIII-3 - 1. I use both single point and expansion. I also have my depth of field button remapped so that when pressed and held, the AF switches from One Shot to AI Servo.
Good luck with either lens on your 7d, you will enjoy either.
