You say your work commute is your main riding time and you want to ride more twisties and track days...are you sure? Don't feel pressured into the other venues if they're not your thing, just because everyone else has a 600 ss and rides the twisties doesn't mean you have to.
Seems to me like if you wanted to ride twisties, having a katana shouldn't hold you back and you don't need the latest greatest track special to enjoy them.
I love riding backroads and the highway is pretty lame but some people love nothing but highway, some like nothing but track etc etc.
Try a naked standard, suzuki sv650, yamaha fz6, maybe even a motard like a suzuki drz 400sm, shit loads of fun, extremely capable on back roads, badass track toys, without the hardcore race feel and temperament of a 600 ss.
If you're just asking about brand, I've only owned 2 suzuki's and loved both of them.