I love tire threads.
Mostly because, as a retired lawyer, I admire polished BS.
And, of course, I am always prepared to toss in my own feeble and foggy anecdata to the mix.
But, kidding aside, purely technical tests, even when unquestionably objective -- hardly a given -- are not especially helpful. I am not entirely sure that the "numbers" alone, even when accompanied by the comments of an experienced rider on a machine I'll never ride to limits I'll (hopefully!

) never see are particularly useful to me.
Instead, I much prefer what one gets on rider forums, especially as here, that focus on one motorcycle.
Naturally, we are all different in size, shape, weight, experience, "daring," etc. after etc., but this is all way more helpful to me -- even when disagreements arise -- than are charts and "real" data.
So, with that in mind, I have to chime in and vote with those who find the Metzler (Z6 OEM on my 2010, anyway, and also delivered with my Norge) disappointing in virtually every aspect that matters to me. They seemed (to me) to have cooked away in the first 1500 miles whatever their out-of-the-box performance that came with them. The rears (and, a slow learner with the three sets I put on the Norge) corded at 4K miles.

Mileage is way less important to me than performance safety, but it is not insiginicant.
Interestingly, I found the Pirelli AST's (on Norge and GRiSO) not much better except in staying "fit" longer.
I try very hard not to be a "Ford, Chevy, or Dodge" sort of brand-loyal guy, and willing switch to whatever seems right. Despite that, I do find myself gravitating to Michelin motorcycle tires for my stable.
The MPR3's were stupendous on my Norge (and lasted 7K or so), and I have had it at the limits of my competence window (a small piece of glass, btw

) in all sorts of road, weather, and load conditions.
So, when it came time recently to reshoe both GRiSO and Norge, I went with the MPR4. "Regular" for the GRiSO; GT for Norge.
In retrospect, given what (I think) I know about compound mix -- MP3 = SMS & MP4 = MHM -- perhaps I should have put MP3's, rather than 4's on the GRiSO.
I have about 1K miles on the Norge's new 4's now, with zero signs of wear on front or rear, and the handling on wet and dry, two-up -- and with all the of the 6-week-safari accoutrements Kathi brings along! -- has been confidence inspiring.
I only have about 200 on the GRiSO, so jury is still out, tho I intend to ride it to Illinois for roller work in two weeks, so will have a better idea then of how the beast handles in the great roads between here and Athens, Ohio, before the cornfield flats begin. When I'm droning for 400 miles between cornfields, I'm sure I'll appreciate the hard centers.
Bill