Blessing of Fervor and Slow

[Pex]

Haste and Slow dispel each other. How does Slow interact with Blessing of Fervor? Blessing of Fervor is a buffed up Haste that doesn't stack with it. Slow was created long before Blessing of Fervor so naturally would say nothing of it, but Blessing of Fervor says nothing about Slow. Do they dispel each other or only partially nullify. For example, you could choose the extra speed option of Blessing of Fervor that cancels Slow penalizing speed but you're still staggered and you just want a move action anyway to move your normal speed. Likewise because you're staggered from Slow you can't make a full attack to choose the extra attack option of Blessing of Fervor, but since you're still allowed one attack you could take the option of +2 to hit, AC, and reflex saving throw.

For simplicity the DM decided they dispel each other as with Haste, but we would like an official answer if there is one.