Twin BB 400hp GT25's from garret would do you fine for 400rwkw but a single GT35r with 0.82 exh a/r would possible be pushing close to 2 bar to push out 400rwkw tho? dont take my word for it tho as not to how the GT35r's are with 400rwkw.. waiting for a few people to get there car tuned.... *cough* 55nat
dont forget tho.. if a big single can do the job.. its easier to pay for one turbo and a waste gate instead of 2 turbos or 2 turbos and 2 wastegates... either wat your choice.. personaly i'd prolly go with the big single.. have you looked into a HKS T51R KAI?
Waz