I wore out a 70 ME880 in 10,000 miles, and currently have 8,000 on a pair of Stone 850/851 Z rated 70s. Liked the Metz, Like the 850. The 850 may be just a little smoother, but both are good for me. Love the handling, the smoothness, the stickiness, and the water traction in both tires.
I expect to get about the same mileage out of the Stones as I did the Metzs, but the price is a lot less - HDLs $212 delivered during this sale VS the nearly $300 for the ME 880s.
I will add that the 70 series seems to give less mileage than the regular wing tires - I got about 12-13000 out of each set of ME880s 60 series, and cannot get that from the taller ones.
But I now have 3 new sets of G850/851s in the garage ready for wearing the bike out.