We used to pack around a 75 qt Canyon, but have found this past year we do just fine with our 22 qt. It boils down to how much real estate you want to dedicate to your cooler. You know your height limit, so start shopping. Do note that I work in the recreational outdoor industry and you can find much cheaper cooler options that will perform at the same level as a certain over hyped named brand.
I have an older coleman 200qt and it doesn't fit under anything. I'm willing to say it performs at least as well as a certain over hyped brand for about half the price. But at 2 feet tall and the width of a JKU rear cargo area, it leaves just enough space for 3 5gal jerries. But did I mention half the price and none of the bro's.