I bought a 57 about 2 years ago. A great hat. That 450 regulator is very easy to breath at deeper depths, and is very durable. It doesn't freeze up in cold water like the 350. Best hat ever, and I've dove them all.
lots of dives in sl17, 27, and 47. the 17 is the 'superleak' and i'm sure you can figure out why... The 27 and 47 both have the new locking mech. and you'll stay really dry, but the 47 with the REX reg reathes REALLY well! It is, however, a much larger hat... have not dove the 57 yet.