The Metzeler fronts tend towards cupping, from what I gather. Mine had it when it was getting worn out, and at any speed really if I let go of the bars and thus took away the damping that is the rider, the bars started shimmying back and forth. I can only imagine what it would be like at 100+ mph, never tried that with those.
The new V-rated Cobra whitewalls Triumph commissioned for the Thunderbird LT that I put on the bike this season took away any tendency to shimmy in any way. Haven't taken her past 105 mph with them yet but with a 19-inch Clearview plus lowers the bike was rock solid at that speed. Of course, I also upgraded the rear shocks to Progressive 444's, that did away with any minor wallowing tendencies I felt in curves, so maybe it's a combination of both better tires and better suspension, but either way the handling of my Touring now is absolutely immaculate. Well, ok, still need to do something about the front-end dive but it doesn't seem to affect handling all that strongly, just comfort.
I'm sure I'll put some Metzelers back on the bike soon. All it's going to take is a madman with a gun to my temple to force me to buy them instead of more Cobras...