Are Productivity Modules useful in Pumpjacks?

Productivity modules and beacons at first is best if you can produce sufficient oil with the pumpjacks you have. (If you can't meet demand, may want production modules + speed beacons) The amount of production it has before reaching its lowest point is limited - so you want productivity to make the most of it before it is gone.

However, once it reaches its lowest production (20% production of initial yield, or 2 oil per second, whichever is higher), you want to switch to all speed to maximize output. The oil is unlimited at this point, so productivity has no benefit over speed which will get you greater output.