Do you play a lot of games on your phone?

The benchmark should be: How long can the phone run Pokemon Go before the battery dies.

I play tons of games on my phone but it's usually only games like Solitaire and similar 2d games.

It would be interesting to know if they were just reimplmenting Android's View OnPaint and doing it in 2D land or getting an OpenGL context and drawing it 2D in there. I wonder what the battery differences would be like.

Do people play a lot of graphics intensive games on phones?

I do and the battery only last an hour. We need bigger batteries. CPU speed is never the issue.

Naive question: do faster cores perform slower tasks with more efficiency? In other words, if a game uses 80% of the old processor, but only 50% of the new one, is there an impact on the battery life just by being a faster CPU?

Yes. Especially with multiple cores, gets more work done quicker and the core can shutdown. The core can also scale down where it is presumably more efficient.

It is definitely becoming more common.