The majority of my use came in the 5-12x range, although I played with it across the full range. A few times on the rifle I had gone too far on mag, and it was fast to spin back to a reasonable zoom while still on the gun. I did not notice a change in image quality or resolution regardless of mag. I can't definitively answer where the box stopped being visible, as once I dialed back below ~5x my eye switched to using the thick posts to center/bracket the target. I had very little flat range time with this scope, almost all of my time was at ranges from 300 to over 700 yards. Low-light resolution and contrast was great, the 460 yd target in low light I referenced was shot on ~9x.