Let me describe my situation first:

1. Currently on 6th year of H1b due to expire on May 31st, 2011.
2. Green card application is under process. Labor certification is approved and i-140 application under proces to be approved within a month under premium processing.

I'm looking to change employers as soon as my i-140 gets approved to make use of the FY11 H1b quota (which I will need since I am transferring from non-quota H1b to quota H1b).

My question is that can I file the H1b transfer as soon as the i-140 gets approved or should I first file H1b extension with my current employer and then after that file the H1b transfer with the new company?

Also, in either case, would the H1b be extended for 3 years?