I have both a 600 and a liter. I'd say go with the 600. Sure there is a power difference, but the 600's are better handling and stuff. I would never get a bike that has been down. Sure, it looks like it's just cosmetic damage, but I've seen two people lay bikes down going less than 10 mph, and it tweaked their forks bad, wasn't noticeable at first, but you could definately tell.
Xstriker has a point, you will probably lay down your first bike. The majority of people do. I have had eight sport bikes since i was 16, and have yet to lay one down. But if you look it my track record for off road bikes, you will see why. I have a lot more respect for street bikes as pavement looks like it will just hurt a lot more than dirt does.
If you are worried about power, or outgrowing it, I can promise you, chances are you will never out grow a 600. The newer ones anyway, like 06 and up, of almost any make. Also, most of the 600's have a lot more advanced stuff that comes out more quickly than the liters, such as electronic steering dampner and stuff, which is amazing. The reason is, 600's are bigger sellers than liter bikes due to higher insurance rates, then being a few grand less, and people don't need the extra power. Seriously, the difference I feel in mine is up there, but there is only so much yo ucan do on a liter bike. Sure twisting your wrist in almost any gear and having the front wheel up is great, but only when no one else is around. 600's will still come up as well. And there are hardly any cars out there that can out run a 600, either off the line or top speed.
Last thing I would do, try to find a sport bike class around you. 1, this will lower your insurance costs. 2, this will help you be able to turn at slow speeds. Sure, everyone can ride a bike fast around a big open corner, but how many people can do a figure 8 on a sport bike in a 13 foot space? Good luck with whatever you buy.