Wow....

Well the ZX6R is definitely a nice bike, but I am big fan of the 636 the 05/06 model year was probably the sexiest ninja ever created.
The GSXR600 is an extremely nice bike, my buddy had one and I would say it was sick.
The Yamahas are alright, but I don't know about buying a bike from a company that makes guitars haha

On a seious note any newer 600 is going to be more than enough power

I have an 06 ZX6R with just a few mods and it's just as fast if not faster than my Cobra. These bikes are no joke and unless you have experience I would not recommend starting on anything bigger than a 600.

Oh and I would also never buy a bike new again, too much $$ you're throwing away.

Just my .02