I have a 100-400 but at times wish it had a wider aperature and at times find the 100 a bit long.
As an alternative I am considering selling it and buying either 70-200 is or without ( funds dictating ) and a x2 extender. With the extender I will have a very similar range to the 100-400 and retain the auto focus. The big advantage is without the extender I have the 2.8 and arguably better image quality. The downside would be the price.
Has anyone here had the same thoughts??