Highway riding on a GZ250

[supersquid]

The original reason I wanted to ride was to be able to hit the highways. I got a GZ250 because it was cheap, had good reviews, and was a great starter bike, but now that I have enough experience and skill to own the highways I'm worried my bike can't keep up. It's a totally stock 2001 GZ250 (except a dent on the tank and some scratches where I laid it down in the rain). How fast can I cruse on the highway without jeopardizing the bike? What mods would be easy and worthwhile so it'd be a little better of a highway eating machine? The kid I bought it from said he never really rode on the highway so I don't have any advise specific to a GZ250 yet and the guy at the dealer was useless. Any advise from y'all?