During the day, both binoculars should be equally bright, as the human pupil is only 2.5-3mm in size anyway.
The advantage of the 8x42 should only become apparent at dusk or in very poor visibility.
I presently have EL 8. x 42 and NL 12x42 on my desk.
The 8.5 is most definitely the better in brightness terms in poor light. On a sunny day however I cannot perceive an appreciable difference between them in terms of brightness of image.
Although it took me a few days to get used to the NL it is a fabulous device. What it isn't, in my opinion, is light years better than the EL. It is more an EL Mk2 really. Subtly better (especially ergonomically, FOV and in the focusing) rather than a huge leap.
Note I have not looked through the other glasses in the NL range, only the 12x.
If relatively light weight, good handling and 12 power are what you seek over the last ounce of bright image on cloudy days, then the SL seems a good choice to me. Certainly I have found the 12 x to be really transformational in the pleasure of observation. You just see so much more detail.