Exhaust Questions

Hey guys, I'm in the middle of a budget build on a 88 635. Just got all the parts for the 5 speed swap and am trying to layout a plan for the exhaust. I'm going to try to change as much of the stock system I can, But my question is... has anybody experimented with removing the cat. and how does it affect the o2 sensors. I have been doing some research and the euro models didnt have one and therefore had a little more power and from what I read, ran alittle better. My brother did a build putting a non vanos m50 into his 87 e30, when he did his exhaust somethings up with the cat and makes this crazya** sound, probably a shot baffle? Just trying to avoid this from happening. Any help is great!! Thanks

i replaced my cat with magnaflow cat universal and 3 inch single pipe cat back and 6x18 magnaflow muffler and dual tipps. warning a bit too loud. more then i wanted it

My B&B Triflow with a cat is just about right. I thought about removing the cat but have not done so yet.

So when replacing the cat. Did they come pre drilled for o2 sensor or did you have to drill it? My sensors in the cat.