I asked this question because I found a new 120/90 ChengShin C822 Marquis for $10. It doesn't fit under the fender - but I pulled the front fender off and it barely fits. I've got about 3,500 miles on it now and it looks like it will go 10K. It's a bit slick compared to the other front tires that I've run, but the roads are dry now and it will be OK. I'm pretty happy with the price per mile, so I might burn up another one of these berfore the fall rains start.
I was running a Kenda K671 150/70 on the rear, with it, but I had a tire failure at 10K. The Kenda was wearing really well and it looked like it would go 14K to 15K before hitting wear bars... I e-mailed the Kenda people and they are sending me another one free. Yea Team! The K671 is a six ply and should easily handle the weight of my K1200RS.
Right now I'm running a Metzler 160/70VB ME55A on the rear. It seems to run well, but I only have 1,500 miles on it so it's too early to project tire life. The only significant difference that I've noticed is that between the oversized front and oversized rear tire, the tires rest lightly on the ground when I'm on center stand, and give the bike just a little more tilt on side stand. That's good.