I ran a set of T63s on a 1100 on/off road ride in Mexico last year. I snowed on us in the mountains for the first 200 miles, so wet and a little slimy; they worked better than I anticipated. Further south, it was hot with lots of deep sand. As long as you kept moving, the rear worked OK. The front was fine in all conditions.
The only flaw was that the rear started to rip at the base of each knob. It didn't rip through the carcass but I really had to be careful for the last 300 miles as not to destroy the tire.
Bottom line; I don't think the rear holds up well on a 950/990 due to the HP and wheel spin. My buddy has a set on his KLR and they worked really well so I'd say on a lighter lower HP bike, no problem. I don't know how they would do on a street-going ocean liner GS 1200.
If it flys, f*cks, or floats... RENT IT!
'06 KTM 950 Adventure S
'07 KTM 450 EXC