1 to 1 1/2 inches should do the trick. I beaded quite a bit in Alaska, particularly for Dollies, and was closer to an inch. It was totally effective and would almost always result in the hook getting sucked into the mouth as well as the bead - occasionally there'd be one hooked right on the outside portion of the mouth, but never any further than that.
If you're fishing the bows in Alaska though, go streamers, the bigger fish are almost always taken on streamers (or mice). Now, for dollies though, glo bugs and beads just can't be beat - they are following the salmon runs up to scarf eggs. I've even heard aggressive dollies will head butt female salmon to get eggs to spit out.