I tend to only wash my hair once a week, and it does fine. My hair is very dry (even with conditioning, etc.), so it doesn't produce a lot of oil that would otherwise make it unmanagable.
And to be completely honest, (and hopefully not gross anyone out here), I just washed my hair on Friday...it was two days shy of being a full two weeks. It was behaving so nicely, easy to braid, easy to bun, easy to comb....I didn't see any need in messing that up. It didn't have any odd smells, or otherwise look raunchy, so I just left it.
I don't think I could go much longer than that, but it was an interesting experiment....
Good luck with your findings!