To clarify my statement a little better
They say on a non-1series that no AF over F5.6 but that is not exactly true. Before I bought my 100-400 is tried out ::John::'s one. I could get it to AF at 400mm on the 30D but he couldn't on the 5D in the same conditions.
My 100-400 will sometimes AF around the 250mm mark (on the lens) and up to 300mm on a bright day but I cannot say what the F stop was then, but it is definitely not reliable. @400mm it is definitely no AF in any conditions.



.
