I'm not an optics expert by any means. But I do have some good glass (binocs, spotter, etc.). The 6x42 has an excellent field of view and is clear. I don't see any chromatic aberration. The eye relief is also very good. Only complaint I have seen, and that I agree with, is that the Mil Quad reticle is pretty fine and might be hard to see in low light. I know guys get great hits in very low light beyond 200 yards just by centering the target in the box defined by the heavy top and side arrows.
I've hunted with a fixed 4X for years (as well as with variable scopes). 6X seems about perfect for me, and I would say out to 600 yards it is just fine for shooting, not spotting. I could see some people having an issue identifying a specific buck in a group at long distances. For my terrain (Lowcountry of SC), I'll take the fixed every time and would also be happy to take it out to 400+ yards. 400 is about my limit of confidence, not the limit of a 6X.