A reference for Question2: (from Q.W.Fleming " Earned Value Project Management")
Dr. David Christensen-study of 155 contracts 1971 to 1991:
1. Cumulative CPI stabilizes at 20% point; 2. At 30% point variances only +/- 10%; 3. At 40% point variances only +/- 8%; 4. At 50% point variances only +/- 7%;