at 10k per minute you're at ~600k per hour. That's a healthy amount of messages but well within the capabilities of the Kiwi engine. I'm not sure how you identified that it's 250k messages behind, I don't recognize that buffer info.
What database are you writing to and how? Is is with the Action 'Write to Database'? Are you also logging to disk? How many rules do you have and how far down the list is the rule that writes the Barracuda logs to the database?
When the message is displayed in the console it's hit the syslog engine for processing so I would suspect any delays are on the writing side.