from what i have learned most exhaust shops carry only 40's they all say you cant hear a difference. one of my friends had a 44 then jacked up his exhaust 4wheelin replaced it with a 40 and he said he cant tell a difference maybe if you heard them side by side but thats about it i have 4 magnaflow cats with 3 in from the y pipe back going through a 40 series and it has a real nice rumble but not overly loud. although my neighbor said they can hear whenever i come and leave. i bet you my neighbors love me lol, loudish expy bronco with longtube headers and cherry bombs and a corolla with trd exhaust all my vehicles rumble haha