Why not have a high-performance games machine for playing games and a regular low power PC/laptop for less demanding applications? I assume you'd spend the bulk of your computer time with the latter.
I just got a Raspberry Pi 2 and I'm impressed with what under 5W of computing power gets you (not that impressed with the on-board audio though). Not saying go to that extreme, but a capable laptop will do fine with a few 10s of watts.