I'm from the dark side but this may be helpful:
I mounted a brand new set of TKC80's on my KTM950 4 weeks ago. I have about 1/4 wear on the rear right now and I've done a total of 1200 miles; of which 300 are dirt; of which 250 was groomed dirt and gravel roads. That leaves about 50 miles of what I would characterize as mud, rocks and dryish ruts (lots of spin). All of the dirt was with loaded panniers. My highway was mostly Interstate @ 75 cruise.
My TKC80's are the new 150/18 size designed for the 950 KTM. That means they are more robust (and alot more money) then the 140's. I am guessing they are designed for HEAVY bikes like the TKC's for BMW twins.
As a point of measure, I am attempting to pay close attention of my TKC wear because I am running a time/speed/distance event in August that will likely require a tire change and am restricted to just 2 tires as spares. I am pondering 2 rears or 1 front and 1 rear. Hope that helps, but I'll know more in 3/4 weeks. -P
Straight ahead and faster -Bo Weaver 1970
"There I was..." -Griffin Niner Three Hotel
"One day closer to a parade..." Jonny Gomes, spring training 2013