iSeries journaling performance

I am responsible for a legacy application deployed on an iSeries V7R3. The application is fairly high volume, 2 million or so transactions per month. The database for this app spans multiple libraries and I am currently journaling each library individually. I've been looking on the web for suggestions as to whether this is the best approach or if a single journal for the application might be better or at least be just as efficient. So far I haven't found any clear advice on this topic, with some advising separate journals for each physical file. Of course searching for anything about the iSeries brings back ancient results often with no mention of the OS version or date of the information. I'm not experiencing any problems other than managing multiple journals is sometimes a pain.