When to apply for new visa, if the current visa is active and I already have extension approval?

My current H1B expires on Nov 1 2014. My extension petition has been approved (Nov2 2014 - Nov2 2017) and my revised expiration date is Nov 2 2017.

I am going to India in August 2014 for a wedding. If I apply for my 2nd term visa in August while in India (with the approved petition starting Nov 2 2014), will they allow me, or is too soon?

And if I am coming back to the US end of august, then will my I-94 bear the stamp of Nov 2017 (new date) or Nov 2014 (old date)?