Personally I'd skip the T3/T4 stuff and go with a Garrett GT28RS with a 0.64 A/R turbine housing. I'm pretty sure it uses a T3 flange for the manifold, but it's internally wastegated so if you use a manifold set up for an external wastegate you'd have to plug the hole. Much more responsive and produces a wider powerband than any T3/T4 variant, even those with ball bearings. It ain't cheap though.

The "remain reliable enough as a third car" part of your original post is what has me a little befuddled though. You'd have to run an electronic boost controller with high and low boost settings because I wouldn't want to be running 20 psi of boost on the trip to Taco Bell or whatever.