What methods do companies use to identify high performing employees?

It actually depends on the industry and management, so a specific method might not suite all industries. but there will be guidelines which are globally accepted. Like meeting the expectations and requirements, involvement in company growth and achieving goals in timeline etc.

but more specific methods will be applied based on industries, like production per shift on a production based company, sales targets in trading compalies, and successful activity records in contracting and construction companies.

360 degree performance evaluation method.