I'm with Ryan 100% on this ... a 600 is more than enough bike for you, especially if you have no experience on bikes. My first bike was an old 82 CB650 and when all my friends just twisted their wrists to go fast, I learned how to use a powerband and carry corner speed to keep up. That and when you dump your first bike, you'd rather it not be a nice new litre bike.
For the life you get our of your bike, it's all about how well you take care of it. Of course some bikes last longer than others, but with some TLC you can have yours last well over 50 000 like Ryan said.