There are many factors to consider when determining whether to file a new petition. For the EB-2 category, in addition to you having either an advanced degree or a bachelor's degree plus 5 years of experience, the position must also require an advanced degree as a minimum qualification for the position.
For September 2011, the priority dates for all countries are current in the EB-2 category, except for India and China. The cut-off date for India and China is April 15, 2007. Assuming that your I-140 has been approved, you would be able to retain your EB-3 priority date of September 2008. If your home country is India or China, your priority date would not be current yet.
You have raised some very good questions and I urge you to contact an experienced immigration attorney to review your options.
Best wishes,
Mark
Answered on Aug 31st, 2011 at 1:20 PM