It's normal for the boots to hang over by maybe a 1/2 inch or so. And
it also depends on your stance angle. As was suggested, try taking the
boots and bindings and see how they work on the actual board you're
trying to buy.

All good advice...

... I *would* be very surprised to see size 10's hang over the edge by
anything close to half an inch on a "normal" width board, that is between 24
and 25 cm at the waist. IMHO the ideal overhang for a reasonably advanced
rider is generally 3/8" - 3/4". Beginners and intermediates who don't tip
the board much on edge can get way with more, as can someone who uses
risers. I personally have size 8 Salomon boots and using a 26 cm waited
board (wide, but not *that* wide) gets me 3/8" overhang at all corners.

What's interesting is how many people say "1/2" overhang is best" and then
you present them with a board / boot combo that yields 1/2" overhang on all
4 corners and that say "that board is too wide".

Sorry if I am confusing the issue, but it is a confusing issue

In any case the "put it all together at the store and get it up on edge"
method is what I recommend, if it is feasible to do so.

Mike T