We enabled auditing very recently, so we plan to move auditing data to an archiving database every month.Also... you don't want to be keeping audit data in your production database. You want to routinely move it to a reporting database.
You did not say if you already do this or not. But I have seen enough audit enabled databases in the wild to be of the opinion that you are probably NOT already doing this. Feel free to amaze me by saying that you are the exception!