I have always been a firm believer that the majority of MSPs are incapable of holding boost over 10psi on stock internals, without an excellent tune and supporting mods. Shoving the boost up to 15psi is openly inviting trouble.
However, there are those few 'factory freaks' out there that seem to respond just fine to whatever sort of mod-nonsense you'll throw at them. I think my MSP was one of those. I ripped apart my entire engine bay (EXCEPT for the block), drove the car with a broken WGA twice (which had the boost flirting with 20psi before I caught on and backed off the gas pedal), drove the car with a lean tune for a couple days (long distance Unichip tune FTL), would have to deal with MAF-induced seizures thanks to the MAM FMIC kit (magnumP5 knows what I mean!), blah-blah-blah .. ran about 10.5psi for years, and the engine was still going strong the day my MSP was totaled. With 92K miles on it! And hell, the damn engine still STARTED and RAN the day I went to rip off all my aftermarket parts in the junkyard. I couldn't believe it.
For the masses, though .. I highly advise caution. Unless you really know what you're doing, or are fully prepared to accept the consequences of blowing your engine (amongst other things) -- I would NOT push it too far past 10 or 11 psi. Nothing annoys me more than seeing people whine over blowing their engines when they didn't take the proper steps to safeguard their blocks against it in the first place!
