Cat delete

I've heard many different opinions about losing the cat in a e36 m3
will it be worth the money to buy the o2 sensors? how much power will it gain with a cat back exhaust? THanks

Which O2 sensors? The front ones yes. the rear ones only monitor the function of the cats. They rarely go bad... no reason on earth to remove the cats on a street car. Replace them if they are bad.

How much power from a catback? Almost none. Weight savings are another story.