Yes, but you're still looking at this 1 dimensionally. In the narrow scope of your argument, you are correct; take the same engine, bump displacement a bit and naturally you get more power. However, in the grand scheme of making horsepower, displacement is not the be all - end all, and i think a lot of us here are arguing different sides of the same thing.
I'm not going around saying throw a 2.0L turbo in the GT because with enough boost anything can be fast (even though it can), hell, i traded my 500 whp turbo 4 cylinder in because i wanted just some all motor simplicity. To just say "displacement always wins, every time" is just wrong though. Look at the 3.7L V6 making the same power (or more) than the outgoing 4.6L V8... yes, DOHC vs SOHC, 4v vs 2/3v but that's exactly the point ... The replacement for displacement is technology and innovation. Now, before someone goes and says "well put that same technology into the V8 and it will be better!" Yes, we know that, a child knows that, but keep reading and understand the full scope of my argument.
Take The BMW 4.0L V8 making similar power to the Chevy ls2, Coyote... Yes, it makes a dismal 280 ft/lbs of torque, but it uses gearing to make up the difference, and barely loses to the coyote in the 1/4 which has 100 ft/lbs more. There are clever ways to get around whatever "short comings" a particular engine set up may have, and that is exactly what all of us are trying to say about the GT. In some people's minds there is only 1 way to go fast, and that is the biggest possible engine, with the most possible horsepower. On the flip side though, you can downsize the engine, which saves weight, allows a more narrow, aerodynamic body, with less material that also saves weight. Now since the rear is smaller and the overall body is lighter we can get away with less bracing and lighter suspension components, which helps. Then on top of all that the car needs less brake to perform, so that is downsized and lightened ... its a snowball affect where little things keep adding up and the end product is greater than simply a sum of its parts.
I dont think anyone here is strictly saying a v6 is better than a v8, we're just saying it is better in this particular application.
