H1B Extension on ending 6 years for time spent outside country

[Kumar61]

I am on the 6^th of year H1B, and my GC labor is getting ready to be filed in 1^st week of December. Meantime my 6^th year of H1B is ending on 6/16/2013. Now my attorney is asking to file for an extension for 5 months which I spent outside the country. During that period we are expecting that labor and I140 will be approved.

Need your suggestion on the 2 options,

1. File an extension by end of Dec 2012(less than 6 month) as processing times for such case can range from 3-5 months. – Is that true? Will H1B Extension takes 3-5m months to process?
   
2. Wait until April, and by beginning of May 2013 file an extension one month prior to expiration of 6 years of H1B (6/16/2013) - Is this option is feasible? If so what challenges I can face if it is not approved by 6/16/2013? Am I still eligible to continue to work past 6/16/2013 based on the extension filing? Is this option is feasible or more risky?
   

Appreciate your suggestions\ comments on this.