Node-webkit is basically the Google Chrome browser (strictly speaking, Chromium). It has node.js features as well, but we don't use them much with Construct 2 (yet). It seems to work a lot better than Awesomium for us, even though they are supposed to be very similar.
Both Chrome and node-webkit v-sync their display. So if you get 59 FPS, in some circumstances it will get worst-case v-sync interaction and fall all the way to 30 FPS. So it's likely the difference is actually very small.