BobD,
It always seems to be a question of 'over-gunning' yourself. I've looked through many pairs of 8X and 10X El's and a number of SLC's in the field. Clearly to me the EL's were better optically. I didn't notice so much of a difference with ergonomics. But, ergonomics is very important. I've also had brush fits on the side of a hill because I could see deer in early light with my naked eyes, but not in the undersized bino's I brought along to see the deer more clearly. The weight factor isn't so much as the useful/uselessness of an item you've carried for a full day and can or can't use when the time comes.
That said the biggest difference you're gonna find is at dusk and dawn. Dawn being the most important in hunting use, because you can see where the deer are. At dusk you can only see what you missed a chance on. The clarity of a lower power is very important. I have found that taking 12X and 15X bino's into the field is difficult. Because you need a rest of some sort to look through them and see what you want. You are also limited by the field of view. Higher power also limits light transmission through the optics. To put it in western deer hunting terms, where you'll need to reach out a half mile quite often, at dawn when you start getting to be about where you want looking over herds moving to bed down, is when you'll use them. So best light transmission that you can afford is critical. You may be on the move, so too high of power is out. It should be anyway in the field. Unless you need to see some finer detail for some reason. In rifle scopes I always say, you need to shoot center-mass, not the second button down. But, if you are looking for the trophy that gets away year after year and need to see antlers clearly, then you might want to go to a higher power.
When it comes to clarity in difficult light situations, the El's are better than the SLC's. But, you have to decide how difficult the situation is to warrant spending that much money on bino's. If you are an afternoon birder, or tend to glass through the lighter hours of the day, you won't see what makes the difference. And, won't need the difference the EL's would give you over the SLC's.
