From what i know it is relative to the particular regulations of the country.
Aust Regulations state the following: these are ICAO compliant as far as i KNOW so regs around the world should not vary too much.
ENR 1.5 para 3.2
Unless otherwise specified, holding procedures are subject to the following limitations:
a speed: IAS must no exceed
1) up to and including FL140
-230 kt, or
-170kt for holding, limited to Cat A & B aircraft only;
2) above FL140 up to and including FL200, 240kt; and
3) above FL200, 265kt.
Note: above the highest MSA in turbulent conditions, speeds may be increased to the lesser of 280kt or M0.8 subject to ATC aproval in CTA.