Canon RF 100-300 f/2.8 IS USM

[Joel Eade]

Here's a quick comparison, and I think the 100-300/2.8 + 2x holds up very well compared to the 600/4 II. The 100-500 is no slouch, either...

https://www.canonrumors.com/forum/th...-is-usm.42653/

In those images, I would agree. Those are more of a "bird-scape" style .... my preference with birds to have the subject much bigger in the frame in which case the new 100-300 with the 2X TC may do just fine. Since I already own a 600 f/4 and the RF 100-500 it's not really a lens that's on my want list although it is clearly a stellar piece.