Upgrade from Canon 7D mark II

Hi all,
I have been shooting Canon 7D mark II + 100-400 IS II for more than a year, and generally speaking I`m Glad with the files. Before that I shot Nikon ( both aps-c and FF ) for 4 years.
I shoot mainly birds and love action and in flight photography.
Now, where I`m not getting good results is in AF tracking against low contrast BGs., even sometimes the AF with perched birds in low contrast is a hit and miss scenario.
Second thing is when I don't expose the frame properly to the right, and I want to recover the underexposed file, this degrades with noise artifacts to an extent that I send it to the trash can.
So my observation and experience are making me to look for an upgrade.
I shot a bit with Canon 5D mark IV and Nikon D500 ,both gave super nice files. One way is going up in the Canon lineup , but it is super expensive ( 3.300 US ) and the other is switching to Nikon again.
I would like to ask to the experts the following ;
Have someone had the chance to compare both cameras in the field with BIF ? ( I only took some pictures with both cameras of stationary subjects. )
Does it really worth it to go FF with Canon 5D mark IV , taking in consideration , the downsampling process of cropping a frame ?
Any ideas , I welcome gladly.
Thank you
Marcos Baumann
Santiago - Chile

I have never shot wit any Nikon so can't advise you there, but if you choose to go with the 5DIV you will get a definite improvement in tracking, a more assured focus 'hit' and if you use the mk3 1.4xtc you will get all-points f8 and avoid the 'crop factor' issue.
Having said that, in my experience after about ISO 1600 the pixel quality means almost all of the 'crop factor' is negated.

Marcos,

I had shot with the older Nikon gear(had D3S/500VR for a while and also tried out the D4 a few times) they did not compare well with Canon for BIF and the lenses were old and heavy. With new D5 and D500 I have heard the AF has greatly improved and D500 is now probably much better than the 7D2 which in my experience had poor AF for BIF tracking. Furthermore Nikon now has the FL series light super telephoto lenses that can compare with the Canon's offerings, although they are more expensive and also don't perform as well with the TC's which you will use often with a FF body. Overall Nikon finally has strong offerings for BIF shooters

The choice you are facing is mostly a lens choice as opposed to a camera body choice: If your budget is limited there aren't any affordable lenses on the Nikon side that compare with your 100-400 MKII. Some folks use the super zooms (some third party) but the results are not acceptable to me in terms of IQ, those may work if you are not critical about sharpness.

Good luck

Thanks for the tips Mike

Thank you Arash.
If I go Nikon I would buy a 200-500mm f5.6, It is the only lens that I know, that rivals the canon 100-400mm IS II in the category.

The sharpness of that lens isn't quite as good as the 100-400.