I tried running my game in iOS8 Safari - WebGL was running great! I think it was managing to maintain 60 fps whenever it wasn't loading music.
Audio in general seemed pretty buggy - still needed to tap the screen to start sounds, and music seemed to either drop out/not play/not loop at times... but I didn't test extensively.
I have a feeling Phonegap will be the way forward. I'll be using CocoonJS for the initial release of my game, but I think future updates (and future games) will all be using Phonegap. I have the confidence now
Bonus: being a paying Adobe subscriber/customer, I get Phonegap unlimited for "free"