As a new rider myself who started on a CB500, I can say my first experiences on our freeways here in Portland were similar; and we have speed limits of 90 kph. Part of the feeling for me was the buzziness of the bike at those speeds (it sounds like I'm flying!), combined with the wind gusts from trucks and general traffic navigation and congestion. It can be quite unnerving for the first time rider, and I still do feel like a little "leaf" when taking it out on a freeway. The other unexpected contributor was doing it on a naked bike; wind pressures even at 90 kph are substantial if you've never experienced them before. I do agree that either the 500 or 550 has plenty of power to keep up with traffic at any speed.
The other factors I mentioned above are what drove me to try out a larger full fairing bike for super slab riding. I went with a BMW R100RS, which has a full fairing, steering damping, and is geared for high speed cruising so it doesn't sound buzzy on the highway. Now the CB500 gets to go around town and on back country roads while the R100RS gets high speed cruising; and with the advantages it has, I arrive a lot less flustered. The advantages from the full fairing alone are substantial; when you remove the buffeting effects of the wind from speed and from vehicles, the experience is MUCH less daunting.
There are guys that commute on their 500's and 550's every day. I guess I'm not an iron butt in that regard.