You don't have to worry about a specific picture mode to achieve low input lag for gaming on the Vizio P Series - they can all have a good one. However, the choice of HDMI port does have an impact. We used HDMI 5 for our tests. We selected the Calibrated mode as a base for our calibration.
Here is a rundown of the features available on the Vizio P Series:
This is the result of our 11 point grayscale calibration. Unfortunately, this won't translate well to other panels, so we don't recommend that you copy these settings for your own TV.