Funny, the Linux kernel performs excellently on my $35, 800MHz, 400mA ARM RaspberryPi embedded machine, my x86 desktop, and some of the world's largest supercomputers with who knows what architecture.
For a company with hundreds of millions to spend on R&D, you'd think Microsoft could match a bunch of hobbyists.
I am as big a Linux fanboy as anyone - but Linux doesn't do power management across different set of hardware consistently and when it does it is with mediocre results. In fact you'd be hard pressed to find a PC Laptop running Linux that gives you great battery life. It's largely a miss. So performance yes, great power characteristics no - that's too hard due to sheer number of variables.
For a company with hundreds of millions to spend on R&D, you'd think Microsoft could match a bunch of hobbyists.