Since Awesomium supports WebGL, C2 games render on the GPU using WebGL.
Then, due to the architecture of Awesomium, it sends all the pixels of the final rendered game to the CPU. So we just turn it around and send it right back to the GPU to be displayed. So every frame is pointlessly sent to the CPU and back. This makes performance dependent on the CPU<->GPU bridge, which I don't know much about, but is hard to find specs for and can vary widely depending on the system often which unexpected performance results. (In fact, unexpected results in performance testing are pretty much to be expected!)
We've known about this since we started using Awesomium and have been encouraging them to fix it. Luckily, they've already tweeted that they're working on it
, so it should be fixed in the near future. Then Awesomium should render at least as fast as Chrome, or faster.