Garrett's official site for it:

http://www.turbobygarrett.com/turbob...S_739548_1.htm

And compressor map:


So as you can see, you will be off the edge of it well and truely at 400

A 2871 one though, is very comfy at 400bhp:
http://www.turbobygarrett.com/turbob..._472560_15.htm

Map for it:





If you dont know what to look for on the map, click here for a guide to reading them:
http://www.technical-forum.com/vauxh...urbos-t92.html