p.s. Preview would be a progressive action, not a neutral one, since the user would need to Save to finish the process flow of making an edit.
This is an example of why I think having the two states is potentially too big a burden on the user. In your scheme, Save and Preview would each be a large colored button, one green and one blue, correct? This seems potentially detrimental, since they're right next to each other, and thus would seem like they have the same priority.
On login right now, we're using something like the scheme you proposed, but the visual hierarchy is really really obvious because of the placement in the vertical form. It's a login submit button and then a CTA.