[Joshua Bunn (Joshua)]

Thanks Dennis, That is impressive.

David, thankyou. That's dissapointing to bump the focus... I wont be using it for birding.

So, I think I have narrowed it down to the 400 f5.6L and the 70-300 f4-5.6L IS.
So bellow are my considerations:
So the 400 f5.6L appears to be a tak sharper but i dont know if this will be noticable over the 70-300, it's got slightly more reach for sunset shots etc. fine for astro use also.

The 70-300f4-5.6L IS has more flexibility in FL for portrait shots and every day use on travels, has image stabilization, im not sure on its astro performance or whether i may want some more reach for composing sunset shots on my full frame 6d. Note, I wont be shooting birds but maybe some wildlife in Africa.

So im slightly leaning towards the 70-300 for its versatility. I would have gone for the 100-400 f4.5-5.6L IS USM but it looks like the 70-300 has better resolution....

Any other experiences or opinions?

thanks!