Holding speeds are defined in your flight manual for the aircraft.
Those speeds are for the design of the protected area around the hold.
There are a hellva lot of aircraft that's Vmo is less than 230knts below 10k.
Nobody cares what speed you hold at in a hold as long as you stay in the protected area.
And if anyone wanted me to hold at 230knts at sub 14k I would refuse because it would burn stupid amounts of fuel for no reason.