I pretty much clench exclusively. My weight limit is usually 2 oz. Length has a lot to do with it, that stem/shank act as lever arms. As the majority of the weight in in the bowl, the further out it is, the more difficult the pipe is to clench. So most of my pipes are 5 /12" long or less. I like a wide, thin mouthpiece. The mouthpiece has more effect even than the weight. I hate the ones that are thin and oval, nearly impossible for me to clench.
The carvers I favor make nice mouthpieces, comfortable clenchers. Rad Davis, Jose Rubio, Ryan Alden, Larrysson and Cermak all know how to cut a stem and drill a pipe right.