I won't argue with anyone who won't face facts. You may have outrun a GTS, especially an older one, clueless driver, who knows, but I call BS on keeping up with a Turbo. As far as "magazine fast" goes, the first Google search I find for a 2011:
http://www.caranddriver.com/reviews/2011-porsche-cayenne-turbo-test-porsche-cayenne-review Says 0-60 in 4 flat and 12.4 @ 113 in the 1/4. They are that fast. Drag Times has several in the 12's and a couple older non Turbo ML63's at low 13's/high 12's. New ones are MUCH faster. I don't know if your track is at 8000', those Cayennes were broken, or maybe you're the only one there who knows how to drive.
You also don't know much about MB's. ML55's were not that fast. I know, I had one, but they stopped making them 10 years ago and they only had a normaly aspirated 5.5 V8 with 355HP. An ML63 will run circles around one.
This isn't a dick measuring contest. I like these trucks, that's why I've had a few including a modded 6.2 Tahoe pretty much the same as your Denali, but if you want to play with the big boys (X5/X6M, AMG's, Turbos, blown Range Rovers, especially new ones) you'll need a blower. If you guys think you can add 100-200 HP to these trucks and talk reliability, I've got some bad news for you. Yes, it's cheaper to go fast in these trucks, but you hope to keep up or out run STOCK factory hot rod SUV's, and then with a few mods, they will eat your lunch anyway. It would take mega dollars to try to make a Tahoe/Denali outrun these and have the handling, braking, and reliability to go along with it. Relax and enjoy the truck for what it is.