I initially bought an unpowered rack and Mission Gemini 2x12. Which is very LOUD. More volume than I need...
I bought one powered cab and thought it may not be loud enough in a band situation. I have since bought a second powered cab and with both cabs I feel it is more than loud enough. I'll be rehearsing with them soon but I am not concerned about lack of volume.
That being said I think that one cab is loud enough. Once I adjusted the power meter it was much louder as well.