Stock cooling P 2 555 / Athlon same stock cooling, comparison both is depend on which system using!
if u want little OC ( not too Much!! )use Stock cooling :
go bios disabled smart Fan & set enabled Shut down temperature 70C, when your system overheat this can protecting from prevent damage !
Always control temperature !
for more OC need good HSF after market like (hyper 212) + Thermal paste (As5)
How do they compare physically? If the 555 hsf is larger and/or has a larger fan it should cool better. Also, that Athlon is rated at 65W and the 555 at 80W so AMD may have put a better cooler on the 555. They are interchangeable.