Possible Clues:

• To be equal to a horse is most important
• Even number that's very important
• Cardinal's mean on the whole
• Average lot, yet outstanding
• Mean the quantity is of utmost importance
• Even a horse is of the utmost importance
• How an equal sum may be of the greatest importance
• Mean to have a horse that's really outstanding
• Standard volume, but quite outstanding
• Illicit lover mostly given books superior to all others