Understanding CPA Goal, SmartCPM, and CPM for Popunder on PropellerAds

[AffiliateNate]

I'm trying to better understand the 3 pricing models for Popunders on PropellerAds, and how they might strategically be used together.

(I realize this might be a lot of questions, so even if you would be willing to answer just one, I would be appreciative .)

1. In what way is CPA Goal "Best for: cost-effective spending"?
2. If CPA Goal really is the most cost-effective pricing model, then why would anyone ever consider using SmartCPM or CPM?
3. In what way is SmartCPM "Best for: testing"? (I was under the impression that CPA Goal is best for testing.)
4. Why would I choose CPA Goal over SmartCPM or vice versa?
5. My understanding is that SmartCPM is just CPM applied at a per-zone level. Why then would we ever choose CPM over SmartCPM? (The advantages that SmartCPM has over CPM are clear, but the advantages in the reverse direction are not.)
6. If I have a CPA Goal campaign that I want to scale, my understanding is that an intelligent next step would be to do so with a CPM campaign. How? (6a. Are we just taking whitelists from the CPA goal campaign and then using that in the CPM campaign?