Hard to know the answer to that. Who would do a back to back with the OEM unit then a Vcam. Either would have much more twist down low than a static cam arrangement.
"Xkalaba" has gone 290 kw with standard r32 GTR turbos, so I'd imagine 33's being capable of something similar.
However, just put a set of -7's/-9's on instead of trying to steel wheel/high flow/muck around with the standard units and call it a day.
Yeah mang. This exhaust was originally made for the owner of Racepace for his own car years ago. Just don't have the space to fit two 3inch pipes beside the diff.