Best option for 400mm @ around 1K USD

I have heard good things about the Sigma 50-500 as being the sharpest of the big Sigmas. I have the 120-400 OS Sigma, & it's pretty good when I nail the focus. I bought the 120-400 instead of a used Canon 100-400. The Canon was £1,000 used, the Sigma was £650 new with 3yrs warranty. I took lots of shots with each & could not tell which lens was used for which image when I reviewed them on my monitor. Canon lenses [& Nikon] do keep their value better than 3rd party lenses.

--
lee uk.
There are old pilots, & there are bold pilots, but there are no old bold pilots.