I just put a Metz 880 Marathon on my '06 R12RT. The stock rear tire size is 180/55 17 ZR; the closest Marathon is 170/60 VR 17. I measured the before-and-after mounted tire diameter, and it is within 1/8". Lotsa deep tread on the Marathon. So far, only 20 or so miles, seems to handle all right, turns in a little quicker. Haven't hammered it on a curve yet, so I don't know if tread-squirm will be an issue, but it never has before when I used Marathons on LTs. At least there is the likely potential for decent tire-life! I can't afford a bike that eats rear tires in 3,500 miles! Of fairly easy driving! Seat-height didn't change appreciably.
Will advise future pereformance and tire-life. I'll prolly mount a Metz Z6 on the front when the stocker goes away.