To add the event ID to a script will need to be used.
Kiwi Syslog can handle, according to the docs, about 2 million messages per hour. That works out to about 550 per second. We average about 600k messages per hour per Kiwi server or about 150 messages per second. Actual capacity varies by the complexity of your environment. We have 90+ rules with many filters and scripts so we like to keep our max below 1 million messages hour. We do see limited spikes up to 2.5 million messages and handle them with no issues.