I love all the "brink of destruction" 18 psi talks. The fact of the matter is that I bet these turbos will do just fine at that boost level for quite a while, if tuners take the necessary steps to ramp down boost over 6k rpm. Mitsu turbos are quite resilient. People have been spinning the CRAP out of them for decades now, making more power than the compressor is even rated for. Is it pushing the envelope? Yes. Is it on the verge of coming apart, highly unlikely. The edge is there to be pushed, that's what the aftermarket does. It wasn't a year ago that 15 psi required race gas and was an "outrageous" tune for a lot of you guys. The number of armchair tuners in this forum with little to no experience outside the N54, and marginal knowledge even on that topic is amazing.
'17 F80 Tanzanite/SS DCT ZEC/ZCP
'14 991 GT3, Sapphire Blue / Black, 11.30 @ 124
'07 997TT 6MT, Arctic Silver/Sea Blue: FBO E85, stock turbos: 5.9 60-130 (now with 656 whp, 700 wtq)