Thanks reinhardius, that was very helpful! I have also been working to a base res of 1280 x 720, it seems to be the sweet spot. It is promising to hear that CocoonJS is working that well for 7 parallax layers.
Just one other question, if I may ask...How did you go about doing your 640x360 res for web mobile? Did you scale all your elements manually in C2 to be half the size or something more automated?
cheers...