You may see some differences inside the store but it just depends on what you're looking for. For instance, the SLC vs the EL comparison. Without leaving the store you should notice a difference in eye relief(EL is better), field of view if there is any, any presence of tunneling, and the swarovision in the EL should be noticeable as well. I think the hinge is better quality in the ELs over the SLCs as well. Some people, a minority of people, are affected by the rolling ball effect of the EL.
I've owned both the SLC and the EL and light transmission between the two is only slightly different, most of the time barely even perceptible. Other factors were what I based my decision on. The eye relief of the SLC did not work for me. Twilight factor (magnification's roll in seeing in low light) was also a big factor for me and is a major reason why I choose 12x binos. Exit pupil size isn't always the determining factor in light transmission, so don't let that number alone influence you too much.
I have not looked through the NL's yet so I can't provide direct feedback. No doubt they're an awesome bino. I already have ELs and my guess is there isn't a big enough difference to justify upgrading. However, if you're buying your first set of swaros and the NLs are in your budget it probably makes sense to buy those over the ELs if they check all the boxes. Then again, the release of the NL has resulted in a price drop for the ELs, and to me that makes the EL an incredible value for a top tier bino.
If you find yourself reading reviews, be aware of who's sponsored by swarovski. People like Jay scott outdoors, the outdoorsman, and others will always tell you the newest is the best. They might be right, but they're also biased.
My guess is the biggest optical difference between the EL and the NL is the field of view. Swarovski prioritized this with the release of the TX series spotting scopes as well. Everyone got caught up on the modularity but even swarovski reps were most excited about the FOV being bigger and less tunneling when working throughout the magnification range.