That profile shows all of the time being spent in script execution. Are you sure that setting a different resolution has a dramatic effect on the amount of CPU being used?

Nope. I'm not the Retina Mac person. I'm gonna guess a lot of sites make the system busy with scripts, they all post 100+% CPU loads, fans go on, system gets warm - just to load them. Every once in a while the go nuts well after loading and I'll see a Web Content process over 100% and just stay there but I don't know which tab is causing the problem, so I usually end up killing the whole browser.