Ron, a couple of months ago I wrote in some thread in BF: "I've long suspected Leica have some very effective optics solutions they keep secret", and received a PM: "... you have a point. [I had a chance to] talk with one of Leica's optic engineers and he told me that they [don't go for] the highest transmission possible for reasons he [didn't wish to reveal].
Several bin makers, incl. others than the "alphas", have, and go by, their own recipes. Most users choose what they honestly like, with stress on the word "like", incl. those who can afford pricier models.
Back to topic, that doesn't seem to hold for some previous vs upgraded models of the same maker, like Z. FL and HT. The fact behind what James says, rocket-fired at us by CJ, won't be contradicted by anyone.
What if the bin one has, or the best one can afford presently, is old hat? To some, as we see, it matters a lot. To many bird watchers, it need not, significantly, at all.
If you've tried a new hat but need to use only your old one just don't try to recall the comparison, and most often you'll lose nothing, in utility or pleasure.
As I type this I have on the table two bins. A Zen Ray ED3 7x43, with its famously good image, and a Nikon EX 7x50, in N.'s optically most basic porro range. When I switch between the two quickly - only needing to look up a bit to see through a window - the ZR is strikingly brighter and sharper. (Though the N. shows better 3D and some colours slightly more anyone would say there's no contest.) But when I just grab the N., to look at birds or bees (note the phrase is literal) or even trees and branches, I see a bright, sharp, wonderful image. I can be fully content with it. Only in a very, very rare instance - I cannot even think of an example - will it not be able to give some detail I seek that the other will.
Another perspective, I think, will be useful here, on bins, and Life in General (since you asked ;-). What does make a big difference, in daylight, is the view through my little 10x25 vs both these. Instantly there's more useful detail! One will easily experience this even with the smaller 10xs, even other than optically the best. The difference in 10x vs 8x and 10x vs 7x is not much in this regard. So sometimes, with steady hands, in daylight, vs a good 10x of any size many will find the 8x42 HT a new hat which is not all that satisfying. And with the 10x42 HT there won't be the field of view many 8xs of lesser optical quality give.
