As I see it, ATC was given the authority to waive the 200 KIAS rule regarding Class C and Class D airspace, but was NOT given that authority for the 250 below 10,000. The "Administrator" for these purposes is someone higher than the controller. For example, low altitude military airspace does not have a 250 knot restriction, but may not be "restricted' airspace prohibiting civil traffic i.e. MOAs.
So, fly 250 below 10,000, unless your aircraft specifically needs to maintain a higher minimum speed. (pretty much the Whale nowadays, but I don't know about the the French Whale), then do so silently. ATC knows what's up if your strip (actually not a strip anymore) shows B747 and you're doing 280 ground speed.
GF
Oh, and if you are operating underneath a Class B (a TCA to BelArgUSA and me) 200 KIAS, please. ATL Approach, among others, will scold ONCE, then send the Boys in Blue after you.
BelArgUSA: Last week we were operating out of ATL, actually PDK, and the chief pilot of the company we were demo'ing the plane to kept calling it Class B and I kept repeating it back as a "TCA". Boy, did I feel old!!