Sam, would you consider these techniques, the first one is used by Cloudfare to optimize pages (though experimentally):
- Package the JS together in one big package to reduce latency. (this one Cloudflare employs to great effect) Async loading (I think you may be doing async already)
- Can JS be gzipped? They are big.
- Https for only the login screen. Safari and iOS don’t cache static resources over https I understand.