Hi all, I am in a very strange situation and would like other peoples opinions. I will give you a rundown on my cameras and lenses first. Nikon D500, Nikon D7100, Nikon 300mm f2.8 vr2, Sigma 150-600mm Sport, Nikon 105mm macro, Nikon 70-300mm vr2, Nikon 12-24mm, Nikon 18-200mm vr. Ok now that's out the way ... here is my conundrum. I do a lot of animal photography (well try at least), and do most of it at long range and sometimes with teleconverters. Now, I have been given a choice of receiving either a Nikon 600mm f4 (yes the monster), or a Nikon D850+grip .. it's not a value comparison by any means .. it's a "WHAT I WILL GET OUT OF IT" value .. does that make sense ?? I would LOVE the 600mm .. but the D850 seems to be a hell of a camera ... but I have heard of issues with compatibility with the Sigma 150-600mm ... thoughts anybody ?