Question about the cat

Just wondering, in montana there isn't any sort of smog regulation or emissions standards, so how much hp would I gain by removing the catalytic converter and just making the exhaust straight through??

2.5in pipe. Mabye 2-5HP

someone had a writeup and said 5whp by just gutting the cat.

i wouldnt' know though and the muffler is the largest restriction so if you dont' change that then you wont' see much.