RHutch;
You have already been shown a lot of very, very good mulie bucks. Congratulations to all the successful hunters on the wonderful examples.
Though you may not have time to look over the prospective buck for too long, sometimes one gets a bit of a longer look with mule deer - though admittedly sometimes from quite far away.
Anyway, one of the ways that we've found make it easier to judge antler size is knowing what the average ear width spread should be on an adult buck in the area you'll be hunting.
From talking to folks in the know I've been given to understand this can vary a fair bit actually from region to region. For instance we're quite hot here in southern BC, so the ear spread on an adult buck will typically be about this:
If the buck's antlers are inside or outside the ears then, one can get a rough spread quite easily.
As well it will follow that knowing the approximate length of the individual ear will give you a quick comparison gauge for tine length.
In the end though in all likelihood I'd be just as happy with a bit of a character rack with a bunch of kickers even if it didn't add to a numerical target - but that's just me. So I'd encourage you to have a good time and shoot a buck that satisfies your personal goals - whatever they may be.
Hopefully that makes sense and is some use to you on your hunt. All the best luck to you in what sounds like a great place to start hunting mule deer.
Regards,
Dwayne