H1B stamping - which I 129 should I use?

[Aravind35]

Hi,

I am planning to go to Canada to get my stamping. This would be my first stamping. I am on EVC Model and I have a Master's degree. I have my first H1B applied in April 2011 and it was approved until August 2012. I have very recently applied for H1B extension and it got approved and the dates on the receipt says that they are from Aug 2012 to Aug 2015. I have got a question now.

If I go to visa now, Will they consider my previous I-129 or the new I-129? and if my visa gets approved (sorry for being a little optimistic ;-)), will it be approved until Aug 2012 or Aug 2015?

Should I go to visa or should I wait until August and go to visa stamping in Aug 2012?

Please suggest.

Thanks

Aravind