IMO, with a consistent mature approach, the 600 is much less a safety risk than the literbike. IMO, no matter how mature one is, with the present day's literbikes being as powerful and responsive as they are, a literbike for one's first sportbike is really rolling the dice.
I'll just tell you my experience (which compared to MANY on here is VERY limited..)
I started with dirtbikes, riding off the roadways and got a general feel for bikes. Then I got a '79 Suzi GS850 (standard issue streetbike). I also rode an '82 Virago (the cc escapes me at the moment..) during this time.
Then I got a Duc '94 SS900, dyno'd at 72 rwhp. (I mention the hp just to make the point that a literbike in '94 was about half the bike that a literbike today is.) Because of the geometry of a sportbike and other 'learner' factors, I lowsided the bike 2 times at wayyy under 5mph. If it had been a brand new bike, the damage would have been upsetting, and I would have felt obligated to fix it. Not to mention that today's bikes have more bodywork, and it's more expensive to replace. If it were new, I'd have had to buy a brake lever, a clutch cover, a turn signal, and a few other nickel and dime items. As it was, I forgot all about the damage and continued to ride, losing no money.
So the way I see it, even with the most mature and adult non-squid approach, one's first sportbike is going down. It comes down to a monetary thing from my point of view. Everything I've said refers to a non-literbike. Literbikes are a different story altogether. IMO, these days with literbikes all having close to or more than 150rwhp, I would say that starting off on one of those is VERY risky. Then the worry goes from dollars to safety.
EDIT: It's also worth noting that the Duc I got at 900cc, had less power than a new 600cc bike does. So even then, it's a very touchy bike, Especially considering how light ALL sportbikes are in recent years.
It would be easier on you and your wallet to get a feel for sportbikes on something older, less powerful and cheaper, IMO.