What testing methodologies do you employ to optimize campaign performance?

I think A/B testing and evaluating statistical significance is obviously the highest fidelity type of testing you can do, but in the startup world I find that the speed with which you can test and learn is limited if you solely rely on A/B tests. I have found that thinking about things from an MVP perspective (minimum viable product/project) can help you learn and iterate more quickly. For example, if you are launching a new type of email program to see if triggered emails do better than traditional nurtures, taking an A/B testing approach might take you one or two quarters to see a significant lift. However, if you are just looking for any kind of initial signal, you could get learning much more quickly if you launch and then iterate on your initial results.