If you can line up the various high end scopes and test them side by side in varying lighting conditions, you'll see that there is a difference between them, but from a practical point of view in terms of optiics, that small amount of clarity is not worth the extra $1000 or so between the S&B and the Zeiss, Swarovski, Kahles, etc. No experience with the US Optics unit, but it is definitely up there in the high end range at the top.
The difference between the S&B is that it is more durable in combat conditions and has much better adjustment controls, but once again, is that difference worth the extra $1000 + more you'll spend on one.
I am buying the S&B for my National Match M1A because I want one and cause it is what our guys are now using, not because it is the most cost effective purchase.
About 10 years ago I had 2 custom rifles built by one of the best gunmakers in the country for a hunt in Africa. I wanted the best for me and my eyes based on actual testing and money was not an object. I spent a lot of time researching and comparing. The best I found for my eyes for my back up rifle was the Swarovski in 1.5 x 6 and 10 years later I can not imagine a better scope for that rifle which is in 30 -06. On my main rifle, and I was criticized for this, I bought the Steiner in 3.5 x 10. Except for the S&B, I have not found a better scope for my eyes.
Steiner designed the scope, provided the outstanding lenses, and Leopold manufactured them in behalf of Steiner. These scopes were over built. They were over priced at $1300+ 10 or so years ago and I suspect that is the reson why they quit making them. You can sometimes find these on ebay or pawn shops for $300 or so. If you find one for that price you will be very, very pleased with it and have something that is very close to the S&B in performance. Definitely better than the Zeiss and Swarovski scopes I have on other rifles.
Just another experienced opinion on a subject that can be debated forever much like the .223 vs 7.62 debate.