In my own experience:
Piquan has many variations, including fist versions (Che style seems to do this as their "standard" piquan, some other lines call this "old piquan"). The fist version strikes like a "hammerfist."
Bengquan has many variations as well, including several different kinds of fists. I suppose that the "beng" part is the force and direction (forward) more than the specific fist shape, which can be changed per the target or situation.