I think it's important at this point to remember that you’re the one who makes the final decision, and you’re responsible for accepting or rejecting speed assignments (among other things). If the controller assigns a speed that’s contrary to the regs or flies in the face of the safe operation of your airframe, you’ve got to reject that speed assignment. The fact that the controller has done something that he or she “may not do” is really a second issue. An issue, yes. Something to be addressed, yes. But the fact that you busted a speed limit may or may not be mitigated by the fact that the speed was assigned by ATC. I think the key here is to do what’s right and advise ATC of your plan…
This issue is covered in the regs as well as the 7110.65 (controller’s handbook), the AIM, and elsewhere. Here’s what the AIM says. I call particular attention to the NOTES and paragraph (h) (and remind you that the AIM is not a regulation, but rather, is meant to help explain the regs):
d. When ATC assigns speed adjustments, it will be in accordance with the following recommended minimums:
(I’ve snipped 1 through 3)
4. To departing aircraft:
(a) Turbojet aircraft, a speed not less than 230 knots.
(b) Reciprocating engine aircraft, a speed not less than
150 knots.
(snip)
NOTE-
The maximum speeds below 10,000 feet as established in 14 CFR
Section 91.117 still apply. If there is any doubt concerning the manner in which such a clearance is to be executed, request clarification from ATC.
(more snipping)
g. The pilots retain the prerogative of rejecting the application of speed adjustment by ATC if the minimum safe airspeed for any particular operation is greater than the speed adjustment.
NOTE-
In such cases, pilots are expected to advise ATC of the speed that will be used.
h. Pilots are reminded that they are responsible for rejecting the application of speed adjustment by ATC if, in their opinion, it will cause them to exceed the maximum indicated airspeed prescribed by 14 CFR Section 91.117(a), (c) and (d). IN SUCH CASES, THE PILOT IS EXPECTED TO SO INFORM ATC. Pilots operating at or above 10,000 feet MSL who are issued speed adjustments which exceed 250 knots IAS and are subsequently cleared below 10,000 feet MSL are expected to comply with 14 CFR Section 91.117(a).
(snip)
A reminder... 91.117(a) is the "250k below 10,000" part of the reg, (b) is the "200k within 4 miles of a primary airport within Class C or D airspace, (c) is "200k in airspace underlying Class B or a VFR corridor," and (d) is "go ahead and operate at minimum safe airspeed even if it faster than (a) through (c) allow."
So, for me (and I've probably already said enough to get flamed here), if I'm working LA departures (and I haven't for a while now) and tell you that I want 280 knots, I'd expect an answer something like, "Roger. Once we're out of ten thousand we'll accelerate to 280." If that elicits a less-than-gentle response from the controller, so be it. As an aside, like I said, I haven't worked LA departures for quite a while so forgive my asking... could this not be a restriction holding you to a speed no greater than 280k after 10,000? To me it looks less like a "go fast" call from LA departures and more like a "go slow" call from LA Center which is being passed by the departure controller.
Finally, keep in mind that on at least a couple of LA SIDs you have a chance of going more than 12 miles offshore and then coming back to the shoreline while still below 10,000. The LOOP and LAXX come to miind. Therefore, even though you've been outside of 12 miles and can accelerate, the 250k restriction will come back when you cross the 12 mile line eastbound if you're still under 10.
Dave