I've been running Metzeler ME88 120/90 x 18 rear tires on my '75 750F since 1991, so here is a little report. The fifth one is worn down to the wear bars and I will replace it this weekend. A picture of it is below.
The first tire went 13,000 miles, second 16,000, third and fourth ones each went 15,000 miles. This fifth one is at 21,000 miles. All were kept in service until the wear bars showed on the surface. All were made in Germany. The manufacture date on this last one is December, 2003 and was put into service in February, 2005. It is interesting that this last tire has lasted significantly longer than the previous four. Conditions have been consistent over the years. Most of the miles put on the bike are commuting, with a lot of freeway time. I ride anytime the road is ice free, so temperatures have ranged from the teens to triple digits. A lot of miles have been in the rain, even snow a few times. As the picture shows, the profile has worn flat from all the straight up riding. Traction is still adequate to drag the hard parts on both sides. As you might expect with the flat profile, the tire doesn't like grooves in the road when straight up, but it is still fine in the corners. I always run 40 PSI in the rear tires.
I picked up tire number 6 a couple of weeks ago. It was also made in Germany in December, 2007. I thought this was interesting because I was under the impression that Metzeler had moved their bias-ply tire manufacturing to Brazil a few years back. At any rate, the ME88 has worked well for me all these years on the 750. Durable, handles well, and traction is more than ample, especially for a so-called touring tire. The last three inner tubes I've used have been Michelins.