BF-21667 has been caused by PERF-2404. The change has made readCmd: true required for find/findOne ops in benchRun() but benchRun() does not support any DBQuery.Option under read command mode. We can have benchRun() support DBQuery.Option.slaveOk in a way that the option is translated into readPreference when we upconvert find/findOne op into find command inside benchRun() implementation.