Remember the higher the service level you wish to achieve, the more inefficiently you will be operating.
99% of calls in 1 second may leave you with staff who are waiting for a call for more than 50% of their day.
80/20 is probably as good as anything. Note that the average speed of answer and abandonment rate do not have a direct relationship with the service standard you have.
As a simple calculation
Call ansd in SS/All calls answd plus all calls abandoned.