Below is the USGA's explanation of green speeds. Hard to believe this continues to be their recommendation. In an Amateur setting, 8.5' is considered fast. HCC greens are rolling 11'-11.5' daily. Under 10ft, would lead to unhappy golfers.
Average speeds:
Amateur Green Speeds
Slow green – 4.5 feet
Medium Green – 6.5 feet
Fast Green – 8.5 feet
Medium Green – 6.5 feet
Fast Green – 8.5 feet
Open and Professional Events
Slow green – 6.5 feet
Medium Green – 8.5 feet
Fast Green – 10.5 feet
Medium Green – 8.5 feet
Fast Green – 10.5 feet