That bike is fine dude. Think of it this way....a lot of people over revs their cars when first learning now to drive stick. If you over rev your bike on a 600 you MIGHT pop a wheelie.....over rev a 250 and you don't get shit besides a little jolt.

Safety wise I think this is a good bike to learn on. I learned on an old 300...or was a 350.....

You will outgrow your bike, but when that happens you'll be much more experienced and 600's won't be a problem any more.