If you're using a blow off tube, let it do its thing. Some krausen may creep into the tube, but that's fine. The aggressiveness of the fermentation will depend on the amount of fermentables in the wort. I've had some vigorous fermentations with WLP007, especially in the RIS I brewed.
By the way, if you're doing a starter, no need to double pitch. Save the other vial for the next brew!