rip0ff

my friend just cut 2 of my cats off and and finished the welding. It sounds pretty nasty but i hear that i lose power and also that i gain. I think the truth is you lose some power cuz a mustang specialist was tellin me how the car likes back pressure. What would be the best aftermarket cats to get for performance wise? Also do they sell cats to replace the 2 on the downpipe also? Thanks!