Re: 250 below 10k. As usual, it depends...
From a UK perspective, as published in the AIP (ENR 1.4), as we would expect it depends on the class of airspace.
Class A: "As published in procedures or instructed by ATC"
Class B: "As published in procedures or instructed by ATC" (but there ain't any!)
Class C: "As published in procedures or instructed by ATC" (IFR) and "Below FL 100: 250 kt IAS; OR lower when published in procedures or instructed by ATC" (VFR)
Classes D/E/F/G: "Below FL 100: 250 kt IAS; OR lower when published in procedures or instructed by ATC." (IFR and VFR)
Appendix 4 to Annex 11 has the ICAO version...basically the same, except it doesn't mention the 'procedures or instructed by ATC bits'.