XF100-400 + 1.4tc versus 150-600mm

Mark Levine wrote:

I am an enthusiast bird photographer currently using X-S10 with 100-400 plus the 1.4tc. Initially I was disappointed in the 1.4tc because of the negative impact on autofocus, especially with birds-in-flight at 400mm. I've gotten better at zooming out to autofocus, then zooming in while tracking. This is at the tip top of my dexterity (retired, in my dotage, and so on) but I lose tracking often, missing many shots.

I wonder if anyone has experience (or could share a conjecture) on what I would experience if I swapped out the 100-400+1.4tc for the 150-600. I suspect that the new lens will be, maybe, a hair better optically and will have similar low light performance. I also suspect that autofocus will be generally better, I'm wondering if improvements would be worth the expense.

Probably it's too early to  get experience with XF150-600 vs XF100-400 +1.4TC. I have XF100-400+1.4xTC and Sigma C150-600 + Fringer ProII. For BIF I use only Sigma because it's  2/3 Fstop faster on long end (and 40mm longer). I think AF in my X-T3 works better with bare Sigma than with Fuji lens + TC, because it gets more light. I use sigma with 1.4TC time to time, and to my surprise AF is not significantly worse in this case.

I believe that new XF150-600 have very fast AF motors and can deliver the best results in terms of AF-C performance with  H2s. So far I'm not going to try this lens, but I'd like to check how H2s will work with my current lenses. I believe new H2s with older lenses should work  better than old X-Trans4 body with the new XF150-600 in terms of AF-C performance.

Cheers,

Artur