Then if you want to see an example of a games running smoothly on mobile using the stock browser (to get a reference), the first ones I'm thinking about are the following :
Sprung fever : http://blog.kodewerx.org/2013/05/1gam-april-postmortem.html
Beyond the horizon : http://jamiegault.com/Beyond/
They run just fine on modern/recent platformrs (ipad2 in my case), but for sure that all depends of what devices your are targeting.
Then you still have the choice to use a wrapper (cocoonjs) that will deliver almost native-like performances, enable full audio support , and will also allow you to deploy your games through the various store.