I had a DRE 6 bay frame with a 15" drop on my Leopard for 10 years and running many low water trips such as the MF at 2' and dropping. The only time the front lower crossbar took a hit was on the Owyhee with my brother at the oars. It bent a bit but was easily replaced. Pretty much all these trips were fully loaded with 2-123 qt coolers, a large t-box and table, another large dry box, 2-Jonny Partner tanks and 2 passengers and all the other crap that you have to bring.
Any clearance advantage because of the larger tubes would surely be negated because of the weight involved. That being said, I had to really pay attention in order to move the boat when needed as it took an extra stroke to gain enough momentum.