take this as a starting point: there is absolutely no advantage to cutting your risers shorter than your shoulders - you can cause some serious damage to your shoulders and back from riding like that for prolonged periods. plus, your shoulders will catch on anything before your bars do, if you're the type that likes to weave in and out of traffic.

onetwentyeight has some excellent advice to offer, per usual. why not ride around with them not cut down for a week and see where your hands end up?