Originally Posted by The Duke
400whp? What's your definition of bolt-ons, everything but headwork/internals? I'm willing to bet 300whp (exhaust/tune. Maybe intake if it's worth it) is going to be the ceiling for the car reliably. Beyond that you're getting into diminishing returns price-for-power, much like our cars beyond a downpipe/protune.
400whp is a bit much on the stock turbo. Lots of people out there running 300+whp/350+wtq on stock turbo with the standard bolt-ons (intake, turboback, fuel pump, IC, and a tune). I can't speak for longevity since they've not been doing it that long. There's a couple running around with 500whp with a GTX3071 and internals.