what is the best way to tell if a cat has let go I noticed my car sounded alot different on the way home but seemed to still have the same power

if the guts have gone, it will be a bit louder and have a hollow type note to it, worse when the cars cold, your engine emmisions light may come on esspecially if its a bf, but only real way is to phisically check it unless you can get an emmision type tester

ok ill take it to a exshust shop if its bad tomoro

are there any rattles from the cat area , any overboosting or flames out the zorst.

get a tuner to check it out first IMO. Stay off the gas in the mean time

Usually it wont boost as high due to the substrate of the cat melting/breaking free and getting jammed somewhere down stream, restricting airflow in the exhaust.