Hrmph!
I've had the TKC80's down to about -16c and they worked well.
I've had the Heidenau K60 Sport M+S' down to about -24c, and they work well down to about -18c before they get pretty hard. Emergency braking at -24c is entertaining; you'll come to a stop, but there'll be a couple black chalk lines left behind.
In any case, if you don't put your bike away for winter, there's no big downside to throwing a set of TKC80's on your sport bike. They grip better in cold temperatures than your summer sport tires, they have enough texture to bite through the occasional snow drift or slush you come across, and raise your chances of making it through a winter of casual riding without suffering a scratched fairing.
Note that the TKC80's are bias-ply, meaning they're more comfortable to ride on but at high speed (think 140km/h+), they deform more with centripetal force. If you have huggers, I'd take 'em off. TKC70's are interesting, not as aggressive a tread, but radial-ply and also M+S rated. Unfortunately, TKC70's don't come in a 180/55 R17, closest you'll get is the 170/60 R17.
