I think there are more reasons to change out the IC piping, than simply for power.
If your LLY has the EGR motor and all that jazz, then a small amount of overall efficiency is gained by changing out the cold side, throttle response slighty increases..I'd leave the hot side alone until you're out of the 30series/s300 sized chargers...unless maybe running a stg2 3794 or a tweaked s366 or sxe363...you want to keep velocity up before the IC and the smaller framed chargers just don't do that with a 3" hot side...in my experience, you'll lose throttle response and gain a teeny bit of lag by doing so...but, you do increase max flow potential, which comes into play on the top end, theoretically speaking you can gain HP but sadly the smaller charger falls off about the time the power increase from the greater volume hot side pipe would become a factor