I actually ordered a GTA intake, but when I was trying to slot it in, even with silicone, it just wouldn't go. I should've kept going but I felt weak! (hungover). After I'd ordered the GTA intake, typically, I found the intake off my GT V6. Having been fitted before, it slotted in much easier, was a little bit shorter and a tad bit smaller in bore diameter. I'll stick the GTA one on at some point.
I think there is a small difference, but it's so small, you think it's placebo effect. I'd hoped for a considerable difference, but as others have said, it's always fun tinkering. Just need to do my driver's door strap and I'm done with anything other than servicing on my GT and 156.
p.s. Gazza- thanks for the guide on your site.