short answer:
holding patterns at the altitude you are are most likely to be at are built to be flown at the TAS equivalent of 210 KIAS with lots of margins for wind, error, nav course width, etc. The protected area of the hold is quite large, you arent going to fly out it.
long answer:
FAA order 7130.3a will tell you how to plot the protected area of a hold based on altitude, speed and distance from the navaid (for conventional nav).
http://www.faa.gov/about/office%5For...ia/7130-3A.pdf