... or bright moonlight.However, an f11 lens isn't going to be much use in anything but bright sunlight.
If you want to get to 400mm, then I think you'll find the 2x Extender is definitely your better choice.I have a 70-200mm F2.8 (non-IS)
If you was to chose a Convertor, which one and why?
I'm more swayed by the 1.4x for the speed and quality, but still unsure.