I had an AFE stage 2 setup, which is the same diameter as the stock lly tube I believe. When I put on the mouthpiece there was noticeable difference.
I know lots of guys switch over to the entire LBZ intake setup because its supposed to relieve the overheat symptoms. Can't comment on whether or not the LBZ tube helps out much. I would bank on your most noticeable change being the mouthpiece.
This is all down the drain for me though, along with the stock turbo. I switched out for an HTT and it was the best move I've ever made for my Chevy. I would recommend not wasting money on mouthpieces etc. Splurge on a new turbo. Performance and response is 10 fold compared to any intake modification I've ever done. I was surprised how dead and restrictive feeling the stock turbo was setup (compared with running the same tune on a new turbo). Then, after I got it dialed in, it was worth the money spent.
If your set on the mouthpiece though, it does make a difference. Spool up seemed slightly better. Seemed more free flowing. Noise changed too... I wouldn't bother with the tube though, for the costs associated I would just modify the stock tube or use an aftermarket intake tube and modify it.
Edit: If you haven't got a mouthpiece already Ive got one. 50 bucks... I don't ship though, needs to be picked up.