You guys aren't listening to each other!!!
In CAS ATC can control your speed or authorise you to exceed 250 kts below FL100.
Outside CAS the AIP dictates that 250 kts is the maximum below FL 100 for the see and avoid principles already outlined.
Like all laws, if you want to break it, it's up to you, but don't ask ATC to clear you to do so. I regularly get people inbound to EGNX at night direct from COA to EME asking if there is any speed control. The answer is always: "Speed at your discretion in the open FIR". Getting caught, by the way, does not mean what someone has termed 'policing ATCOs'. It means running into some poor devil who's out there minding his business and doesn't get the chance to see you coming at 330 kts and you aren't looking out either (Why would you be? If speed limits mean nothing to you, why should looking out for other traffic?).
If you want any convincing, read the AAIB report on the airmiss north of bournemouth a few years back between a 737 going like a rocket and an Aztec doing G/H in the FIR.
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"Take-off is optional, Landing is mandatory"