You are right, I have a letter from the FAA confirming that "normal apeed" means just what FAR 91.117 says; an airplane needing to climb at, say, 280k does not need permission to do so since it is the "minimum safe". Many pilots, not aware of the rules, request "High Speed" in order to fly above 250 for this reason and ATC will often volunteer this permission without it being asked, by using the expression "Cleared Normal Speed".
But lately at LAX, and usually at ANC, I have been given "Cleared High Speed Climb" or just "Cleared High Speed". This without my asking for it.
If the ATC guys do not mean what they say, they should stop issuing such clearances, since most of the pilots hearing this will respond in accordance with their understanding of the English used.
Either that or the US authorities should switch to ICAO procedures...Now that's a thought!