My turbos are from a JDM(automatic turbos) with a slightly smaller A/R rating. Anyway, I dynoed 378RWHP. That was at about 13-14psi and without an exhaust.
Im pretty sure with the exhaust and an extra few psi I would be around the 410-420RWHP area. My JDM is also said to have some internal modifications so 400RWHP is a pretty good target with stock turbos.