I happen to have both currently. The Z3 I bought new from Cameraland last fall. The 2.5-8x36 is a VX-III that I bought new about 14 or 15 years ago and it has been on several different rifles...mostly long action model 70's and Ruger #1's. I think there was a short action M700 in there at one point too. Currently, each are mounted on Ruger #1's which can have eye relief issues with a variety of scopes.

The Leupold 2.5-8x36 has very generous eye relief on the lower half of its power range...4+ inches. On the upper end, the eye relief decreases but it is still okay. On my Number 1's, I do have to cheek crawl just a tad to get a good sight picture with the scope turned up to 8x. It has been a while since I have had it on my M70's and can't remember if I had this issue. On a M70, I did have it mounted with Talley light weights, I just had to turn them in facing each other so that the mounting length wasn't an issue. The duplex reticle is good. Not what I would call "great" for hunting in twilight hours, but okay....and worlds better than the wide duplex Leupold uses in many of their offerings. Zeroing, I still experience some of the random adjustments and have to fire a few extra to get it right where I want it zeroed, but once set, I have never had an issue with it losing zero.

The Swaro 3-9x36 has much more consistent eye relief though it has a slight decrease at 3x and again at 9X. Not significant, but enough to notice if you have an eye relief critical setup (such as a Ruger #1 without offset rings). The eye relief is not nearly as generous as the Leupold on the lower power range but they are practically the same on their upper magnification ranges. The 4A reticle that Swaro uses in their Z3 models is FANTASTIC for hunting in twilight hours. Bold posts that come in close enough to see in the waning moments of light, but a fine enough center section for more precise shots in good light. So far, this scope has only been on one rifle and sight in was short and sweet. A quick bore sight yielded a first shot that was only a few clicks off. Slight adjustment followed by a few groups to check and everything was good so I can't really comment on how reliable and precise the adjustments are on this scope. But I do know that the handful of times I have checked it over the last year, zero has been good.

I agree that the glass is good on the Z3, but I don't know how much you are gaining when comparing 36mm objectives. They are not in the same league as my larger objective scopes where I feel you can better discern differences in glass performance.