At this point it's an argument over semantics. Jeff, from personal experience, has run 20 PSI daily with no noticable leaks but Icedout has heard from Jeff Hill that 16 PSI is about the limit. In this case it's safe to assume that once you get close to 20 it will start leaking noticeably (perhaps). Basically, you'll need some serious mods to run close to 18-20 PSI safely so for this purpose putting a 1g BOV in the 2g is the way to go.

At what point a stock 1g BOV leaks isn't an exact science so let's agree to make 18 the magic number with a +/- of 2 PSI. That way everyone is happy. :)