Max stay on H1 when visa was stamped for 2 years but did not travel

My H1b was approved in 2011 and i got the visa stamping for 2 years at that time through Company A. Due shortage of projects in my company A i did not go to US at that time. Now a company B wants has transferred my H1b in their name and provided me new I797 etc. My queries are:

1)How much is the maximum duration including possible extension i can stay in US on H1b now since i did not utilise my 2 years and never travelled?

  1. My stamped visa expires in 3-4 months from now. I am planning to travel within a month. Is it advisable to travel with the old visa and new I797 or should i apply for a new stamping from company B?

Thx much