All types of warp (crook, bow, twist, and cup) will increase the lower the moisture content, though proper stacking and stickering techniques can help minimize warp. Severe crook and twist, and to some degree bow, will have an impact on the planer's productivity as these pieces may jam the planer. And the excessive warp may exceed that allowed by a particular grade and thus cause the piece to be downgraded. Overdrying will increase the amount of cup, and this may result in planer or roller splits at the planer. Overdrying will also lengthen pre-existing end splits and can also increase torn grain.
I could not find the Milota publication that Tim referred to, but I think the 1% value loss for every 1% MC overdried is a reasonable estimate. So if your Hem-Fir sells at $300 per MBF and you know you have overdried this material by 2% MC, the estimate of degrade cost would be $6 per MBF.
To quantify this in your lumber, you would grade the lumber using your grading rules and give two grades: the first grade is the grade of the lumber in its dried condition; the second is the grade the lumber would have been if the drying defects were not present. A tally of the volume and grade loss and cause of the degrade would be kept. You would need the MC of each piece so you would know the average MC of the test bundle. This would allow you to begin to make an assessment of the cost of drying degrade due to overdrying.