Considering how boost and turbos are on other cars, there really isn't much lag with it tbh, maybe 500-800 rpm later. It still hits full boost fast as hell, you shouldn't be worried about that at all. Also pulls much harder toward redline rather then falling on its face early.
Interested in hearing in detail how you fixed this with PRL, I have those same sounds after just doing careless downpipe and up pipe, sounds iterating, not how my Si should would with 1500 miles..