There are more factors than just HP numbers which are for the most part just hype anyway. You have to factor in the transmission as well as the rear end ratio. I don't care about numbers but in the real world I pulled a fifth wheel with a 2008 F-350 with the V-10 (365 HP) and now have the new V-10 (320) with the new 6 speed transmission in my class A. Even though the Class A weighs more; it pulls the same hills easier and faster and also gets slightly better gas mileage. How much is the engine and how much is the transmission I can't say and don't really care.
I was always told that HP is for speed and torque is for power. With our RVs I feel that power is more important.