If you really want to know how everything works and how to pick a turbo, then you should read these:
http://www.mrcontrols.com/primers/sizing.htm
This one gives you alot of tools to determine what you car needs to do what, and explains alot of what happens. I found it very helpful and went through all the math a few times with 'My' specific numbers to pick my turbo. Dont bother using their numbers, your car will probably be signifigantly different, especially since your working towards 400+ hp.
http://www.stealth316.com/2-3s-compflowmaps.htm
I found that this one has alot of compressor maps about halfway though it and I used it to see closer whitch turbo I wanted, It also explains the maps with colored lines to show you a specific example, but My application was quite different, so I had to kind of overlook the lines.
I suggest that after you find a turbo that is kind of close to what your looking for (probaby one of the ones from the second webpage) that you do a google search on it and see any info you can find on it or any of its closest friends that might also work.
And from what I've read a t3/t4 might be a good choice, you just need to see which size's work better for you. Bigger compressors give you more boost ability, while larger (a/r) exausts generally slow spool time while letting more exaust through; too small an (a/r) for exaust will constrict your engine and thats not good.
Edit: Sorry for the ambiguity, when I was referring to the "size" of the exaust, "bigger" was not referring to the physical size, I meant a bigger a/r ratio.
Hope this helps