Mortar Melon is on the Windows Store and soon to be on the Windows Phone Store as well if it isn't already. It plays great on my Surface RT. One thing that you need to know is that Mortar Melon is a physics/catapult type game. Not an Angry Birds clone, but of the same genre. This means that it doesn't have as many moving sprites on screen at once, but relies heavily on physics, which leads me to believe it is more CPU bound than GPU bound.
But playing it on the Surface means it is basically using the IE engine when I run it and it still performs seamlessly at HD resolutions though IE is definitely not the front runner for HTML5 performance. So not sure how much of a direct comparison you can draw, but HD and running in IE and it still does great.