Well for what it's worth when I called swarovski to ask about the z5 vs z6 I was told the following. First the glass was the same glass however there is a HD coating on the z6, the 30mm tube is more of a rugged scope able to take more punishment, however the 30mm will not let in more light. I was also told that some people who looked through both scopes were unable to tell a difference between the two. Now with that being said I'm not saying that the z6 isn't better than the z5 I just don't feel in my OPINION its worth the $1k more in price for the long range scope
I needed for my set-up. I'm also a nikon fan as I feel they offer awesome clarity, however I will say that in my opinion from 400 yards on beyond the swarovski just blows the nikon away! The long range detail the z5 (5-25x52) offers is amazing.