I had both. Bought a second hand classic (1997) and a new zenith a few years ago. The classic got bdc turrets fitted and a scratched lense was replaced for free by S&B.
When out stalking with my son we had both scopes along. My take, the zenith is way better when looking towards a setting sun. Less internal reflection.
Other than that, not much difference.
Zenith has the option of the flash dot reticule, which doubles as a day light red dot scope. The FD7 reticule is so fine that one can shoot crows at 250yds and with the red dot cranked up works well on running game close up.
The No. 7 reticule I had on my classic was great for stalking. I was absolutely confident to neck shoot deer at ranges with the scope. The fat reticule worked very well at dusk but was not great for target shooting, load developement or shooting a crows at long ranges.
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