15x..... Exit pupil on 20x is too small and from what I remember the smaller the exit pupil the less light let in so low light performance will not be as good for not much gain in magnification and lower fov.
15x if only for the selection. I think Docter makes the only higher end 20s, and they're heavy. Although the 15s lack the magnification to judge in detail over about 1300 yards, they lack nothing when it comes to finding game. I'm going to try a doubler on mine and see if it works out.
I borrowed my father in law's Kaibab 20 x 56 for my Antelope tag last year. I can tell you that they have to be rock solid on a tripod to get anything out of them. I thought that the brightness was fine. The weight is the thing that kills this option for me.
these are 25 x orions and they are awesome. you could count p dogs pups around a mound at 1500yds with no problems. we also have a set of 30x and like them better.
but take note of the tripod. we have tried several 100 to 150 dollar tripods and they were worthless. that is a movie tripod that weighs 18lbs. the binos and tripod together weigh 28lbs. the used tripod cost is about $175 on e-bay. but that is necessary to stabilize the big stuff. i dont have 20x binos but am willing to bet they would fall into the same category like 280AI said.
if you wish to work around the vehicle they would be fantastic. even off a 4x4 wheeler you could cart them around.