From what ive been reading everywhere from people who have them is the extensions hold up to the abuse. Just use your head and dont doo tail stand lands daily on it Im not sure of your location but the 136" is perfect for me. I would never go back to a 121" track. There is not enough contact patch of track on the ground with todays 121" long travel suspensions.
Just ordered rail extensions from black magic and a 136x 1.375 track...gonna longtrack the ZR!! Price wise, i got the track for 600 can. new and the rails for 150 new!! I got all the aluminum to build the tunnel extension for free(i work in an aluminum welding shop) !!Also getting rid of the plastic bumper and fabricating an aluminum bumper for mine as well!! i know we do alot of cross country off trail and ditch banging so i think it will do very well for hooking up in the stubbles as well as the deeper snow....gotta be better than the 121"! I know of a few guys that just used extensions and have never had a problem with them at all and they ride pretty aggressive!!