Few people will argue against that the "Disco Potato (Garrett GT2860RS)is the best streetable turbo for an SR.
I'm doing my research at the moment and have narrowed it down to either the dancing spud, GT2871 or GT2876. In rough terms the 2860 is rated from 350-380 horse, the 71 is 400-430 and the 76 420-450.
These figures obviously totally depend on supporting mods making use of this extra flow capability.
The 60 will be least laggy (basically none) and the 76 will be a big laggy but obviously bigger top end.
To further confuse the issue you could put a bigger turbine housing on the 60 and it may prove to be just as laggy as the 76 but make a similar top end.
The more I read the more confused I get! At the end of the day unless you're making a dedicated drag car the 2860 will be your best option. Either way, you can kiss $1400 good bye!

As a side note, one thing you will need to add to your list of mods is bigger injectors otherwise a bigger turbo is a waste of time and money (and you may need curtains for the windows you just put in your pistons). You should look at 700 cc's as a minimum to leave yourself scope for further upgrades.

I'm far from an expert so consult an expert before spending big bucks but that's what I have come up with so far!

EDIT- I just read your post properly (!) and thought I should add that regardless what turbo you put on you will need to get the computer reflashed or replaced with aftermarket. They have a certain level of self adjustability to changes but won't cope with a bigger turbo/injectors/etc without mods.