[pandaman]

There is 0 difference in the speed of GC process. It does not matter if you are on H, L, O or don't have any status at all and applying from abroad. People are spreading this myth because L1-A and O-1 requirements are pretty close to EB1 so if you can get such a category of visa then you have a good chance to apply to EB1. But, again, if you fit these requirements already you can just apply to EB1 from any status (or lack of thereof).

[klipt]

Actually at least one cateogory, EB1-C, specifically applies to managers relocated from an overseas branch of the same company. An equivalently qualified manager on H1-B in the US is ineligible for that category.

[pandaman]

Equivalently qualified manager on H-1B would have spent a year out of last 3 serving in such a position overseas so he would also be eligible. Alternatively, a L-1A manager who already spent more than 2 years in the US would be ineligible.