Post your best bird shots!

[JJphoto]

Its negative impact can be lessened (and
sometimes removed) at diffraction-inducing apertures, at which point
you're fighting other sharpness loss than the lens system anyway

thank you czeano for pointing that out, never think about that before.

and the 2X extenders reduce AF Drive Speed by 75%

thanks Rich for the information. 75% sounds really bad, but Canon claims that the performance of the TC III in real world won't be that bad if using with their version II lenses and 1D or 1Ds body, so we will see soon.