Document the Velocity and Throughput stories, which are encapsulated in one new chart available in the Performance tab of Workflow Metrics. It's the Completion Velocity chart:
Completion velocity tracks the number of completed workflow instances over the selected time period.
-- Completion Velocity ChartLPS-97665
LPS-98001 More detail on the completion velocity chart
LPS-98233 Custom time range definition on the completion velocity chart
Time period descriptions are here