6 psi is #### all, you could fart 6psi.
step up and put it on 10-12psi at least.
you should never pop a headgasket, unless its pinging, setups not going to ping because you will go out of your way too design it properly.
my bottem end has done 220 000km, it has seen up too 21psi of boost from a gt35
ran on 15psi for 10months, 15 due to clutch slipping on 19psi which it was set at.
boost isnt going to pop a gasket. poor tuning will.
oh btw standard nissan head gasket, standard headbolts.
good surface prep and using a good torque wrench and using the correct toque sequence, do it once do it right.
copper head gaskets along with extra injectors belong in the 1990's leave them there.
running two standard head gaskets is retarded.
use a standard nissan genuine gasket or a cometic, at least a nissan gasket may act as some sort of fuse of sorts in the event of a lean out