I gutted the cat on mine w/ SLP shorties and stock exhaust. I really like the exhaust sound but I guess that exhaust sound is a little subjective to personal taste.
My cat failed and was plugging exhaust flow. To test for a plugged cat install a vacuum gage to intake and gradually increase revs in nuetral, if vacuum drops at higher rpms the exhaust flow is blocked. A partially blocked cat is less obvious power will decrease under full throttle in the higher rpm range.