I have had many 8x56 binoculars including the Steiner Shadowquest 8x56, Zeiss FL 8x56 and the Swarovski SLC 8x56. They are slightly more forgiving because of the bigger exit pupil, giving you more room to move your eye around, and they can give you a little more 3D because of the larger objective as explained from Cloudy NIght's.
"A greater diameter of the objective lenses helps the 3d view by introducing a 3d effect produced by the parallax effect in objects out of focus: a roof 8x50 will seem to show more 3D view than a roof 8x30. Parallax effect in objects out of focus means that, when the shifts a bit laterally, everything closer or farther than the focused object will shift slightly with respect to what is in focus. This is a very obvious effect when using a terrestrial scope like a 20/60x80: when the eye is shifted to, say, the right, objects farther than the focused one shift to right, objects closer than it shift to left. This effect gives some impression of 3D view, and is very useful when looking at birds in the thick of a tree, because a slight movement of the eye helps to see beyond the branch that hides the bird. If I reduce the objective diameter, or if increase the magnification, the parallax effect is reduced. In binoculars, the 3d view can be helped by the parallax effect, especially when eyes don’t stay always perfectly on axis, which is usual with hand held binoculars."
But the major factor in 3D is objective lens spacing. The farther apart your objective lenses, the better the 3D out to about 100 yards. So if you really want good 3D, any smaller porro will be better than a bigger aperture roof prism like the SLC 8x56. Immersiveness is determined by the AFOV and the Swarovski SLC 8x56 has a very average 60 degree AFOV, whereas, some of the newer 32 mm roof's like the Swarovski NL 10x32 has a truly immersive AFOV of 69 degrees. For you, the 8x56 would be brighter in low light, but you would not see a difference in brightness in the daytime except maybe in the shadows. The biggest advantage an 8x56 has over an 8x32 is lack of optical aberrations because of the large exit pupil, they pass the field stop of the binocular and never reach your eyes. For general birding, what do you prefer, the EL 8.5x42 or the SLC 8x56? You have four nice binoculars there. I understand the advantages of big aperture binoculars, but I question if they are the best tool for the average birder. I think the average birder doesn't feel the advantages are worth the disadvantages of weight and bulk. That is why they are discontinued. Here is an older fellow that likes big aperture binoculars.
Size Matters: A Case for Really Big Binoculars Contrary to what some of us would like to believe size really does matter. Flight, for example, imposes strict limits on size. Ostriches...
www.audubon.org