One of my friends just got his I-140 approved at VSC, taking only 20 days. He saied he was informed by his lawyer that a NEW mechanism has recently been introduced to VSC, which allows most of the qualified I-140 cases filed with that center to get approved in 30-60 days. Specifically, VSC divides their staff for treating I-140 cases into two teams, one team directly treats the new cases and the other is still in charge of the old cases.
I don't know if the above information is correct. If it is the true case, I don't know either if other service centers will employ or have employed the same mechanism.