Well, first, riding 4-6 hours on a sportbike is a heck of a long ride. You're going to hurt a little bit, even if you are used to it.
However, your wrists shouldn't hurt at all. You should never really be resting your weight on your wrists. Ride with the balls of your feet on the pegs, except when shifting or using the rear brake. This will allow you to support your body a little more with your legs. Also, use your lower back and your abs to support your torso, so it takes the weight off your hands and wrists. Besides reducing the discomfort you're currently experiencing, it will give you greater control over the bike.
Once you've mastered this, your wrists will very rarely ever be sore again, at least from riding. :jerkit :lol Case in point, I rode about 350 miles last weekend, and had no trouble with my wrists at all. My knees, ass and lower back were a little sore, but no wrist pain at all.