Just to be fair we only have one sample of the 800mm and if you compare the it to the first sample of the 600mm II it is such a mixed bag you can hardly draw a conclusive choice.

BUT, with the second sample it is the same or or better (sighlty worse is some extender/aperture combinations) but given the extra versatility of a 600mm f/4 it's well worth it. A superb lens to be sure.

My only real reservation with the 600mm II is AF speed with extenders, to me an in focus picture slightly softer is much better than the other way around! I basically would never use the 600mm focal length and the 1120/1200mm range would be use very frequently and the 1600mm end with manual focus (I'm pretty good at that anyway) is a big plus for me. But I guess I am the minority?

Any-how I can't afford one right now anyway but am saving hard for one,

Cheers,
John.