You can mitigate some of the perceived speed issues by defaulting to show: false in package.json and manually opening your first window after the full runtime environment loads. More info here: https://github.com/rogerwang/node-webkit/issues/1962#issueco...
What I've found, from my development, is that if you use the node-webkit executable to run the folder without packing/unpacking the app, it's faster. Also, killing the application before launching a new instance/using the already launched instance is faster.