Actually thinking about it now its prolly not worth it.
Both file sizes are gonna be about the same (uncompressed)
The win with png is you compress them, but unlike a regular image the image is just gonna look like random noise, thus will have terrible compression

pre-initialised JavaScript structures
Yes I think this is a better method (+ will use it in the final version), better method cause you know exactly when the mesh has been loaded unlike JSON . Though oddly Im using JSON cause its easier when developing (not need to change your code)