I'm close to 200 lbs, my friend is around 140, add clothing and you're looking at around 350 lbs load in addition to a TourMaster II luggage bag (pretty large) on the back, a Saeng WingTip (slightly higher drag effect on the windscreen), full tank of gas, etc. With that, riding 2-up, I had it up to 105 mph (indicated) and there was still plenty more to go. This was on flat ground. With another friend at around 155 lbs and myself, I had it up to around the same speed (105 mph) on the freeway with a slight incline (very slight incline but not level either) with more speed available.
I don't really know what the top speed is, I'm not all that comfortable with 3-digit speeds, but this should give you some indication.