Robert,
My guess is that you’re using one of the RC builds, which is missing recent optimizations. We will be releasing the GA version of Percona Server for MongoDB (PSMDB) in the very near future. I would recommend that you upgrade to that when it’s available; the performance should be much better. Just to note, we have to accept the limitations of the Storage Engine API, which could limit our overall performance due to overhead.
Regarding logging, you can set the verbosity in PSMDB just like you can in MongoDB 3.x. Take a look at this documentation for more info.
All the best,
Jon