Stimo

Fuel rails are not needed, there are many 500whp sti's out there that run fine without them. Not saying that they are bad to have as i got them anyways, but they are not necessary. The lean condition with cyl#3 is for wrx's, not sti's.
The best turbo depends on what you are looking for. What horsepower level are you going for? What are you going to do with the car? daily driver? track? drag? We need to know all of this before we can give you a suggestion.
My guess is your looking for a good daily driver that has more power with about the same spool. If this is the case, i would go with a Deadbolt 20G. Good spool and with the right supporting mods can get you around 350WHP on pump, around 400WHP on race gas..
If you are going to be doing drag racing, i would suggest the Deadbolt SZ49/SZ55 or FpGreen/FpRed from Forced Performance. (The red i don't really recommend as you have to get the tgv deletes and 3 inch turbo inlet). These turbos spool up a little slower than stock but will get you close to 400whp on 93oct pump gas and around 450whp on race gas. If you choose the SZ55 which i personally went with, expect these numbers a little bit higher.
If you want all out ***** to the walls hp, go with a rotated mount turbo kit (gt30r or 35r). If you do not want this kind of hp, then rotated mount is just a big headache and a waste of money, as you can get 450whp no problem with a stock mounted turbo.