I called Cabelas and ordered several five pairs of binoculars - pretty much maxed out the credit card. I was upfront w/ them saying a with such a potentially expensive purchase, I just didn' t want to " guess" and they were cool w/ it.
anyway, I went out to some property nearby that was similar to the area I hunted at dawn & dusk and also under overcast as well as clear days for about a two week period. For me the main criteria is how well do they gather light at dusk/dawn and how well do they provide contrast. I found the Swarowski EL in 8.5 was the best. I really liked the Zeiss, esp since it was about $400 cheaper, but the Swarowski' s won out after numerous trials in all conditions.
I have found the rule of thumb is get a cheap rifle (since they can all hit a pie plate at 100yds) and the best optics - including scope- you can afford. Here in the south, most deer go nocturnal and your only real chance besides a drive is to catch them at dawn & dusk. The optics REALLY have extended my day to the absolute legal limit, esp in pine forested canopy. I recommend a " real world" trial for something this expensive.