Shock Help

I need to buy shocks for the 66 Dart. I will be doing some drag racing with this car, probably 2 - 3 times a year. I will be driving on the street approximately 1500 miles per year, including at least 2 trips that will be 200 miles each way. I am looking at some racing shocks that are adjustable from summit. They can be set at 90-10, 80-20 or 60-40. There is a side note warning about the shocks that says a 90-10 shock should not be used for street use. So my question is what exactly does the 90-10, 80-20, 60-40 mean and can I buy these and run 60-40 on the street and when racing change to the 90-10. How will the settings compare to a standard Bilstein or KYB shock. I dont mind a very firm feel but dont want to get beat to death either, especially on the front suspension. Looking forward to getting explanations on this.
Thanks
Rodney