Ah, that's a shame about the castings on the IWG housings. Would be nice to see a back to back between the internal and external V band housings. Probably not a huge difference but I'd expect a difference none the less.
And speaking of stock STI turbo, the Perrin test shows that well too:
Pretty much identical below 3k but blows it away above that. Too bad this Perrin test is really our only professional source of info on these. And even so, it was with an older prototype. Only a little bit of info out there besides this test and it's all just random forum people.
Another random note. Indy is switching to this turbo for 2014. In 2013 they used the 6758 so, keep an eye on Indy to see a good indicator on how this compares to the first gen stuff.