SITC's are worth it mate, with the auto. they do reduce the turbo lag effect, slightly, once tuned. they make a difference.
look youve got a nice safc tune already, grab the sitc ($220usd off ebay) and have it installed and retuned.
figure out what sort of boost you want to run and work around that, telling the tuner to work on response, but surely a minimum of 1bar is called for - its not as if you can always use it in adelaide traffic anyway, but its good to have it when you want it.
currently I have 190rwkw at 14psi dropping to 12psi as the muffler is a huge restriction. welding a highflow muffler on this arvo, hopefully, for $80. then fitting the exhaust cam gear wheel and have a final tune tune tune, up it from 14 to 15 and hopefully it holds steady, and Id expect around that 220rwkw mark utilising a freely flowing exhaust (incl adj cam gear) and intake (using return air feed apexi cooler and a cai with pod using snorkel and radiator air guide) with highflow slide turbo, adj fuel pressure regulator and direct battery-fed large fuel pump, z32 afm, sitc and safc. response will be fantastic without doubt.
with the 190rwkw tune she is nice and docile in traffic never building boost if you dont want it (saving fuel), or rips thru to 14psi with a niiice surge in power/torque. a true street sleeper. with the slight increase in boost, highflow Kakimoto muffler and the exhaust cam gear wheel I have no doubt that the Stagea will be a true pleasure to drive, and that turbo lag wont be a problem.
SITC ftw!!11!!!111!!!