It has served me well in the city and on lake shore drive...but I get a little nervous the handful of times I have taken it on the interstate....it seems to go 80 without complaints (although I worry about a 30 year old engine spinning so fast for long period), but once you are going ~70, it runs out of acceleration power for passing.
Funny, there's a guy on my block with a kz400 - your name's not Bryan, is it? Anyway, you're doing 70 on the local interstates, and trying to pass people? My cb400 has a little grunt left at 70; the meat of the power-band starts around there and tapers off at 9500 rpm (98mph) so I can still get around someone, but it would take 4 or 5 secs, so hardly passing with authority. I tend to keep it at around 70, though. I'm really only nervous on I88, where avg cruising speed seems to be around 90 if traffic isn't at a standstill. The real issue for me is fighting the wind - I've got a small fairing I got on eBay, but I haven't installed it yet - hoping that will make it more comfortable. Mostly, I take the Hawk GT for highway riding.