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One important caveat to this analysis is that this assumes the drogue will be pulling the entire rocket. As we see above, the CdS of the drogue and that of the booster section may be comparable, depending on the falling configuration. If this occurs, there will not be tension on the booster webbing, and the drogue therefore will not be "carrying its weight." Hermes' descent under drogue will occur faster. 1 To take this into account, we can bound the velocity neglecting the weight of the booster section. According to the mass budget, the propulsion system plus fin can weigh weigh approximately 58.78 lb = 26.66 kg. Subtracting this from the previous weight we calculate:

Mathinline
bodyF_{D, dro} = \frac{1}{2} \rho C_{D} S V^2 = m_{dry}*g

Mathinline
bodyF_{D, dro} = \frac{1}{2}*1.225 \frac{kg}{m^3}*0.662 m^2 *V^2 = 14.09 kg * 9.81 \frac{m}{s^2}

V ≈ 18.46 m/s = 61 ft/s

This is a little lower than the suggested range, but not unreasonably so. Plus, as I mention in the footnote below, this is a pretty complex system and difficult to perfectly predict at all times. 

1 Admittedly, there is some super weird coupling in this system. If the drogue and mission package start to travel faster downwards than the booster section, eventually the webbing will be fully extended between the mission package and the booster and it will start to pull it down. Then maybe you'd enter some sort of periodic pattern of the webbing jerking the booster down and it falling behind again? I am not sure but I'm going to neglect this from my analysis.

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