Loggin is controlled by the dialog as well as the RuntimeConfig.xml. I would use the dialog whenever possible, especially with Log4Net. Any settings you wish to modify that are not in the dialog, can be modified in the RuntimeConfig file.
Disabling all logging will improve performance in general as educes that overhead to 0. Other performance improvements are really in your adapters and automations. Making sure you use the fewest number of match rules will improve that performance. Using the right ones can also affect performance, but these gains need to be tested to be verified. You should also only interrogate controls you need in your automations.