Two points.

The experimental class is an AMA class. If you want to fly with AMA insurance, you must comply with the rules set by the AMA. The FAA standards are irrelevant. If you don't care about AMA insurance, AMA chartered club fields, etc., then the FAA regs, or lack of them, come into play.

The second point is that the only altitude limit is set forth in an FAA advisory. The suggested altitude limit is 400 ft everywhere. Informing an airport within 3 miles of where you are operating is another issue. The advisory is here:

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/1acfc3f689769a56862569e70077c9cc/$FILE/ATTBJMAC/ac91-57.pdf