I am aware of this GF, but my thought was that if your speed requirement is in accordance with 91.117 (d) and you request permission from ATC (which in theory isn't even required) they will of course say "approved" as a confirmation ? What else would they say? They wouldn't go on babbling about how it isn't necessary for you to ask since it is in the regs etc...
Naturally the correct thing would just be to notify them as BelArgUSA said.