Me personally i wouldnt be pulling a 20ft boat with a small short wheel base unibody SUV. Although it may have enough power to pull it there is a "tail wagging the dog effect," and it will be super unstable if you get into a cross wind, heavy braking or emergency maneuver.
Those maximum tow ratings involve some mathematical gymnastics to publish a big number that's not realistic. You will exceed max tongue weight, rear axle rating and/or payload easily before achieving 7,200lbs.
You really need to be looking at full size SUVs or pickups if you need that much tow capacity. The base model GC has a tow capacity of like 3,500lbs and it has the exact same chassis as the trackhawk. That ought to tell you something.
Yeah my rule of thumb is you want double the rating of whatever your towing.
Things get sketchy at that max limit.