Originally Posted by
GreatWyrmGold
That assumes a constant speed. If the caster spends any time accelerating or decelerating, the peak speed is going to need to be higher. If they spent three seconds accelerating at a constant acceleration and three decelerating, the peak speed would be 1200 mph, and the acceleration would be just over 18 G (thanks, Wolfram Alpha!). That's not necessarily lethal on its own, if you're accelerating in the right direction, but air friction would probably rub you the wrong way.