What's the weight of the ST Maxx in 255/85? Haven't seen it posted. My Duratracs are ready for replacement and would prefer to go to a 255 next time around.
The Coopers are better in every respect except clay mud
I, too, narrowed my choices to the Cooper Discoverer ST/Maxx in 255/85R16 (32.8" diameter) vs. the ST/Maxx in 265/75R16 (32" diameter).
I couldn't justify the cost difference for only .04" in additional clearance, and also the additional cost for a 255/85R16 spare.
I went with the Cooper Discoverer ST/Maxx 265/75R16 (the stock tire size on my Xterra Offroad) and have not regretted my decision. I was able to purchase them from America's Tire / Discount Tire in March 2014 for $160 ea. (plus mounting, balancing, tax, etc).
You have photos of your Xterra?
Get the ST Maxx's and never look back.
S/T MAXX is a neat tread, like them lots, tempted to buy more.
It's likely that the OP has already made a decision, but I'll chime in with another vote for the ST Maxx's. For 95% pavement, you'll get better road manners than the KM2's. And in my opinion, the KM2's shine on the rocks, but not so much in the mud. Lateral traction is poor, and the lugs clear Ok but I don't know if they can match up with that nasty red clay. The ST Maxx's won't be great in mud either, but overall I think they fit the bill better. And the road noise that the KM's will develop over time will have you wishing for the Coopers. I've enjoyed rediscovering all the random drive train noises on my 80 since I installed the ST Maxx's on it (I never heard them with my loud STT's).