your speed sounds about average with the stock kit.
i've gone a lot faster, but haven't officially confirmed my speeds, so anything i say can be disputed, but i can say i blew away about 30 people on an L.A. ride.
my bike's pretty heavily modified, and i'm 135lbs with a 30t sprocket on a 24" bike.
i also ride with traffic in 45mph zones. here's a link to some lousy videos: