IIRC correctly, both 5th and 6th gears are overdrive in the CX-9 six speed tranny.
Even in staying out of overdrive gears, the greatest risk OP runs under under the conditions described is the failure of the weakest link in the 2007-2013 AWD drivetrain, the transfer case. To make matters worse, transfer case failure in these vehicles significantly increases the risk of concurrent transmission failure. The first time my transfer case went up at 20K miles, the trans was spared. The second transfer case failure at 49k caused transmission failure as well. These vehicles eat transfer cases about as badly as they suck fuel. Natrure of the beast, I guess.
My 2008 left the fold about two years ago, but I am patiently awaiting to see what 2014 brings for this vehicle. None of the current Skyactiv powertrains (not even the 2.2 Skyactiv D with the known oil change interval overfill issue) would power a vehicle of this weight and size), so unless Mazda has a rabbit under their hat, the 2014 will be significantly lightened and compacted, or their only other option is to outsource a suitably powerful engine and hopefully a more reliable AWD system.
If I were purchasing today, my vote goes to the 8-speed auto 2013 Lexus RX350 F-Sport, but at $52K MSRP before HUD or radar cruise, it's unfortunately a bit too rich for my blood. I did give Mazda a second chance in purchasing a 2014 Mazda 6 GT over the CVT based 2013 Honda Accord Earth-Dreams 4. I wanted the 3.5 Touring Accord with cylinder deactivation and 100 additional HP, but the belt-driven SOHC non-DI 6 speed with no proper blind-spot monitor and a 60K mile timing belt/water pump interval scared me off, not to mention the discernable shudder in going from 6 to 3 cylinders at certain speed and temperature parameters, and the lackluster front-heavy handling of the v-6 sedan. I don't do CVT's, though Honda seems to be the best CVT to date. The 6 speed auto in the 2.5 Skyactiv G and the BMW-ish drive and feel got my vote, and the exterior styling, interior quality, and true blind-spot got my wife's vote. The weakest link in the vehicle is the cheap Tom-Tom nav, which will probably be rectified with a new pop-up nav in 2015 in the style of the new '14 Mazda 3. We considered the 2013 CX-5, but even in the GT the seats were rock hard, and the additional girth took a notable hit on the 2.5 Skyactiv-G in terms of acceptable power, so we decided to hold off a year to see what Mazda will bring to the table with the next-generation CX-9, though I'm not exactly hopeful. I guess time will tell, as Mazda seems to be taking on a positive momentum post-war Ford into the current Skyactiv direction.