Anyone tried a "test pipe" in place of the stock cat and/or muffler?

I'm interested in noise and performance changes.

Thanx!
Mike

i have straight pipe on my truck now; no muffler either. It sounds awesome. I have a buddy with a LBZ with no cat but kept the muffler. I havent heard his at WOT. Based on what i have read the cat will quiet it down a bit and make you have slightly higher EGT's.