I'd imagine that it all comes down to meat grade. I've had great success doing low & slow on choice grade pieces of chuck. I did a bone-in piece last year that weighed about 12 lbs; and took 9 hrs on the WSM. The bone added a huge amount of flavor, plus I used it to make stock. I think I still have some of that in my freezer.
Later on in the year I did one for a freind, she got me a piece of select grade. It looked okay, but it was far leaner than the choice. That piece turned out much drier than I wanted it to, so I foiled it and added some beef stock. In the end it turned out okay. My freind & her hubby were more than happy with the result, I recieved a bottle of bourbon for my efforts.