Garrett were right to keep the rear the same, that way people could upgrade their older turbo's if they wanted, also less issues ala BW EFR.
I have successfully cloned myself into their target market, having the VQ25det which is low comp (8.5:1) with variable cams to wake the turbo up and good head flow it eats whatever boost the GTX3071 throws at it. I am now at a cross roads though, and only have 3 Garrett upgrade options. GTX3076, GT35, and GTX35 all of which should just squeeze in to the tiny space I have for them under the engine.