pipe size from collector to tail pipe.

I like the sound of 2 1/2" duals myself on a 440 street car.
If I were running a blower I might use 3" pipes again maybe. But not over the axle
again.
I went with the 3" exhaust about 10 years ago and I found my car didn't gain any noticable performance like I had hoped. Just more noise. I bent it up myself on a new programmable bender my boss bought and wanted us guys in the shop to get familiar with.
Got the system for the cost of the pipe. It ended up being a lesson learned for me.
I ended up taking them off because of how loud they were. Had to buy more 2 1/2
and do it over.