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The heading tags are supposed to define a document heirarchy. Use the W3 HTML validation tool to generate a bullet point list of your headings. If that list does not look like a summary of your document then you are abusing the heading tags.
Is there evidence to suggest - for the same content - that a page using h1, h2, h3 does better than one using h2, h4, h6? I'd like to think there is a small benefit, but I would guess that Google understands that most sites would not use these elements exactly as they are meant to be used.