you could be right stefan, im no canon user
and all i can say is that i have found no difference if the af/os is on the shutter button and not the rear af button,
i use the rear af button as its easier to recompose shots when needed and also saves changing af modes to afs, and it saves constanly focusing when its not needed, And also saves the os working when not needed and saves battery.

I have had 2 150-500mm and 4 170-500mm and in my op the 170-500mm is sharper wide open at 500mm than the 150-500mm which needs stopping down to f8 to be about the same sharpness,, and also the 170-500mm is lighter and easier to use.
As for the 50-500mm os i have one at the moment and in my op i find it slightly sharper again than the 170-500mm but at f8 its razor sharp.
and the os is about the same as in body in my op(just helps seeing it in the viewfinder)
and i have not used the 80-400mm tokina but have heard good things about it.

it has on, off, and panning, and if you set the af to focus on just the back af button the os will only work on half shutter then, instead of all the time.

and was your shots better than his, thats the main thing,

go into the menu and c1 option 3 extended sensitivity, turn on and bobs your uncle.

i 2nd mike, 170-500mm is only 1.3kg and is the lightest of the 3,

i would go for a 150-500mm or a 50-500mm or even a 170-500mm if you can find one it gives more range for bigger game and closer subjects and also birds and other smaller objects.

there are lots of od noise removal prorames, but the best ones do cost,
neat image is great as you can download the profiles for each camera and it does it all for you.
i also use topaz denoise, and noise ninja, and noiseware pro.
all are very good.

oh and a nice set.

how close did you get to it with the tamron.
the bigma focuses about 10" at 200mm

nice shots, would be nice to see them both used with matrix meterin so the exposure is the same.