As promised, here's the pictures and measurements. 7,000 miles of riding (in 4 weeks), almost all of that on Interstate highways. Trip was Toronto - Alabama - California and back via same route. Speed averaged 75 MPH (70 in the east, 80 in the west). One rider of 180 pounds, 50 pounds in the saddlebags.
I'm very happy with how these tires handle. I didn't have much of a chance to try them out on the twisties, but they certainly handle very well on the superslab, especially on poorly maintained roads, scarified pavement, etc. It looks like I am going to get much more mileage out of these PR4 GTs on my ST 1300 than I usually get from Metzeler Roadtec Z6s on my 1100. For sure, the PR4 GTs handle at least as well (if not better) than the Metzeler Roadtec Z6s on the highway.
What is interesting about the "before and after" comparison is that although both tires have worn by the same amount (2 mm over 7,000 miles), the 'flat spot' is barely visible on the front tire, but normally visible on the rear tire. In other words, going by visual inspection only (no measurement), it appears as if the front tire has hardly worn at all.
Michael
PR4 GT Tread Depth Measurements - new
PR4 GT Tread Depth Measurements - after 7,000 miles
Front - only the faintest evidence of a center flat spot, detectable by feel but not visually
Rear - a flat spot has developed in the middle, but it is not so big as to make a handling difference