I don;t think size 10 boots should be a problem on most regular boards.
I wear a 10.5 and have had no problems on Sims or my Burton Custom.
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.