I think, that will make longbow bit overpowered, to compare it with rus bow. Longbow is slower and less acurate, then you'll need to find extremly build for it, but in reward you get these extra damage. I'm also just reminding, don't try to be superstars, if longbow is too hard or not in your "style" get rus or horn, both are great too. I don't like ideas about increasing speed and making it more accurate. But the solution which Rumblood said, is good I think.