[davidmanze]

I only can judge from what that source posted. And your own observation compared with your 500mm f4 lens appears to confirm it: the Tamron does lose more focal length than that Nikkor. Of course, closer to MFD the Tamron will lose even more.
My point was clear and simple: If you want 600mm for the narrow FOV at close ups, it does not quite deliver. That has NOTHING to do with f11, just was looking into what you said about shooting close ups, and commenting on that.

Judging from the figures from the digital picture dot com, the Tamron does not have awful focal length loss, though.

I have nothing against the Tamron 150-600mm G2 (other than its weight), and do not have any reason to prefer these new Canon primes either, just trying to keep arguments fair and clean.

  At least digital dot com tallies in with my findings then!!

  ........ and I never said that F11 had any relationship with FB!

I'll wait to see the prices of these lenses ........ if they're affordable say ..... $1,000 for the 600mm and $1,500 for the 800mm ..... I'll give them my partial blessing ..... partial only!