If you are talking about a Garrett GT42 the S400s are a whole different deal. Anyone that is used to running Garrett stuff will tell you that .9 is "WAY TOO TIGHT". I have played with .9, 1.0, and 1.1 housings on 83mm turbines and know that Travis has played around even more with different wheel sizes. The .9 on an S400 will act like a GT42 with between a 1.06 and 1.15 housing. The 1.1 acts more like a 1.3 would on a GT42.
I tested the S400/75mm a couple years ago. Trust me, the 1.1x works just fine. It was about a tenth slower than the Garrett, but had better streetability.
