Here is what I have.

Pacesetter LTs
3" piping to make the "Y" pipe (actually they remain separate until an "H" pipe with 2.75 reducers right before the STOCK muffler, with no cats.

Whats this going to sound like?

Would I be better off running smaller diameter pipe from the collectors to the muffler?

I am hoping it will be on the quiet side with no drone in the cab...

 

With the stock muffler I'd expect it to be fairly quiet, even without the cats. It will be louder than it was, but not obnoxious I'd think...but I'm just guessing. I wouldn't run smaller diameter than stock pipes...if the designing engineers decided that 2.75 was good for a stock LQ9, it definitely won't be "too big" for a modded one IMO.