It's supposed to be the fastest human creature made spacecraft ever.
RA, thanks for the ping! I'm a bit busy right now (on our next projects, not New Horizons), so I'm still catching up on threads.
As for the speed, yes, the launch speed of New Horizons was faster than any other spacecraft. The wet mass (including fuel) was under 500 kg. However, the Voyager spacecraft have a faster final velocity due to multiple gravity assists. New Horizons is now going faster than it ever will, and is gradually slowing over time.