Just upgraded to Chrome 57 (Windows). The background CPU usage has gone down dramatically.
On my main desktop which is a lowly dual core AMD FM2 chip, I would see Chrome using up most of the CPU when I had a few tabs open. I was even contemplating installing an AMD A10 5800K I bought months ago to help ease the problem which I had been too lazy to install.
With this new Chrome release CPU usage has gone down dramatically. In fact while I should still install this new CPU I can defer it now :-) Chrome has become more usable, especially on content rich sites and/or when there are a number of background tabs open.