I can give an honest opinion based off owning the scopes mentioned. I have a ZEISS V4 6-24-50 and 2 5-30x50 V6’s. All on 6mm CM. I also have 1 Leupold VX 5HD 4-20x52 on a .243. I’ll say the Leupold has the edge on brightness over the V4 and V6. BUT, the V6 lasted a few minutes longer on the resolve chart. A strange thing to see. Almost as if your eyes are deceiving you. You can see more with the Leupold and see detail a little longer with the V6. I’m not sure on this, but it appears the V6 does have better glass than the V4 by a decent margin. At least to my eyes.
All are excellent and do what I need, but I prefer the Leupold VX5 HD by quite a bit. I really like my ZEISS products....but I had to send one of the ZEISS V6’s in right out of the box for a failed parallax knob and when the new one returned, I had a canted reticle within the first 10 firings with the Ultra Mag. With that said, ZEISS Warranty and CS immediately took care of both scopes. They have always had the best CS. Since then I’ve been a little reluctant to use the ZEISS on bigger calibers. Especially with muzzle brakes. I do have some smaller VX5 HD models and they all perform flawlessly. IMO, if you can swing the little extra $$$, the VX5 HD would be my pic. I honestly think it’s a much better optic than the V4.