I think the US permits speeds above 250kias beyond 12nms from the coast, but I can't find the reference. Anyone?
If I recall, it is simply the lack of 91.117 applying at a certain point.
§91.1 Applicability.
(a) Except as provided in paragraphs (b) and (c) of this section and §§91.701 and 91.703, this part prescribes rules governing the operation of aircraft (other than moored balloons, kites, unmanned rockets, and unmanned free balloons, which are governed by part 101 of this chapter, and ultralight vehicles operated in accordance with part 103 of this chapter) within the United States, including the waters within 3 nautical miles of the U.S. coast.
(b) Each person operating an aircraft in the airspace overlying the waters between 3 and 12 nautical miles from the coast of the United States shall comply with §§91.1 through 91.21; §§91.101 through 91.143; §§91.151 through 91.159; §§91.167 through 91.193; §91.203; §91.205; §§91.209 through 91.217; §91.221; §§91.303 through 91.319; §91.323; §91.605; §91.609; §§91.703 through 91.715; and 91.903.
(c) This part applies to each person on board an aircraft being operated under this part, unless otherwise specified.
So, 91.117 applies all the way out to 12 miles (91.1(b)), but then drops off. Of course, then there's 91.703...
§91.703 Operations of civil aircraft of U.S. registry outside of the United States.
(a) Each person operating a civil aircraft of U.S. registry outside of the United States shall --
(1) When over the high seas, comply with annex 2 (Rules of the Air) to the Convention on International Civil Aviation and with §§91.117(c), 91.127, 91.129, and 91.131;
(2) When within a foreign country, comply with the regulations relating to the flight and maneuver of aircraft there in force...
91.703(a)(1) makes 91.117(c) apply, but you'll recall that 117(c) applies only to "...aircraft in the airspace underlying a Class B airspace area designated for an airport or in a VFR corridor designated through such a Class B airspace area..."
So, assuming you're not in airspace to which 117(c) applies, under the US FARs, that leaves you with Annex 2 (near as I can tell).
Thoughts?
Dave