Hi ;
My milage was around 10,000 kms.
Around 6000 kms was off road and the rest on tarmac. As for sand ride, only a bit of beach sand (maybe 1000 kms )
(+) .. good traction and very good puncture resistance
(-).. slippery when wet and fast wear on tarmac
As for T63, i have no idea.
Note: are you absolutely sure about Michelin dessert 18"? I am pretty much sure they produce that rim size.
Check web site
http://motous.webmichelin.com/home.htm