I hope you are joking, because branding-wise the Steam Machines are a clear mess and completely confusing for people who don't know how to read PC specs. Hell, you have Steam Machines planned with only Intel HD graphics and also called "Steam Machines" just like the Alienware Alpha and the Syber ones, while power-wise they fall in totally different categories. That's the best way to kill your brand, at least 3DO never did that kind of mistake.
> they're generally 1:1 as performant as their windows drivers.
No, this is clearly false. I don't know where you get this impression, check almost every benchmark out therefore for Borderlands 2, CS:GO, Witcher 2, Bioshock Infinite and almost every other AAA game out there, you will see that the Linux performance is clearly behind. I'm a Linux gamer as well but at least I don't pretend we are at the same level as Windows, because that's a clear lie at this point.
> trumping console performance is pretty much a no-brainer with modern nvidia maxwell stuff...
It should be, but many ports on Linux are far from being optimized (some rely on OpenGL 3.x to maintain compatibility with AMD while it's clearly less efficient than OpenGL 4.x calls) while console ports are much more likely to be tested thoroughly on a single hardware based and optimized for it.