Found my old post from 2009, so I don't have to look things up again. On the 2009's the stock radiator cap is rated at 137 kPa (19.87 psi), and the Nismo cap that was offered at the time was rated for 125 kPa (18.2 psi).
Radiator Cap?
On the 2009's, there's only a proper pressure relief radiator cap on the engine side of things (the water outlet on the block). The overflow tank is plastic and has a threaded screw-on plastic cap with no pressure relief.