Why didn't you file for a GC(I-140) as soon as you got your O-1? Since O-1 is an extraordinary ability visa, you will probably file in either EB1 or EB2 categories. Unlike H1-B, O-1 doesn't have a so-called duel intent which means every other time you file for an extension, it's harder to prove your non-immigrant intent. Although O-1 doesn't have a limit on the period of stay, I've heard there is an imaginary 5-year barrier. In case your O-1 extension will be denied, you will have to depart U.S while waiting for an I-140 approval. To prevent this, ask your lawyer to file an Adjustment of Status (I-485) along with I-140 petition. In case of O-1 denial, I-485 will keep you in legal status until a decision on I-140 has been reached. Based on I-485 you can file an employment authorization petition (I-765 is the code I believe) and also a travel document (I-130). Notice, that once a your non-immigrant visa status is lost, you will need to depart U.S. and then re-enter to get it back.