H1B 6th Year with 10 months left. Need GC Filing and also Extension

[indianpride]

My current H1 (6th year) expires in July 2013. If I now move to company X who will file the GC (EB2) and use the I-140 approval to get an extension, will I be able to move to company Y, once the H1B is approved with Company X?

Also, I now have 10.5 months left for my H1 expiry. How long can I wait before moving to a new employer, as the market now is tough? what is the min months on H1 required before a GC (EB2) can be filed and I-140 cleared? I have MS and MBA from this country and work fulltime for a fortune 50 company.