Hey,
the execute watch API allows you to execute a watch for testing purposes via the REST API. See the documentation how to trigger it.
Can you explain the question about performance? I do not understand the intent behind that question.
The throttle period could be set to sth obsene high as 2000d. Another idea might be to deactivate the watch after it was run (or another watch to deactivate all the watches that have been run recently by querying the history).
--Alex