Cummins X15 VS. Paccar MX13- What are you gonna choose?

Depending on your requirements, a larger displacement engine may be the better option. I'm a Heavy Haul/Oversize driver, and I have a new Western Star 49XSB 4 axle daycab. I'm also a major lover of the X15, and I run the 605/2050 with an 18 gear. For me, the X15's pulling strength is unrivaled, the MPG is really rather outstanding for being capable of lifting very big loads, and the downtime has been virtually non-existent. For "normal" weight hauls or even doubles in the 120,000-140,000 range, the MX would certainly enough. But my preference has always been to spec with the most horsepower possible, rather than having to work a smaller engine much harder to get the job done.