Set readPreference @ replSet level?

Can anyone help me with the syntax here: I'm trying to set the readPreference for my replSet and getting an error: so I think I've got the wrong syntax:

replSet = new _m.ReplSetServers( [
      new _m.Server(dbh[0], 27017, {auto_reconnect:true, native_parser:true, slaveOk:true}),
      new _m.Server(dbh[1], 27017, {auto_reconnect:true, native_parser:true, slaveOk:true}),
      new _m.Server(dbh[2], 27017, {auto_reconnect:true, native_parser:true, slaveOk:true})
    ], {rs_name:'rs0', read_secondary:true, readPreference:'ReadPreference.NEAREST',
        secondaryAcceptableLatencyMS:200, strategy:'ping'}
  );
  db = new _m.Db('0', replSet, {w:'majority'});

I'm working off of this documentation (bottom of page) http://mongodb.github.io/node-mongodb-native/driver-articles/mongoclient.html

I can get this working:

replSet = new _m.ReplSetServers( [
      new _m.Server(dbh[0], 27017, {auto_reconnect:true, native_parser:true, slaveOk:true}),
      new _m.Server(dbh[1], 27017, {auto_reconnect:true, native_parser:true, slaveOk:true}),
      new _m.Server(dbh[2], 27017, {auto_reconnect:true, native_parser:true, slaveOk:true})
    ], {rs_name:'rs0', read_secondary:true,
        secondaryAcceptableLatencyMS:20, strategy:'ping'}
  );
  db = new _m.Db('0', replSet, {w:'majority', readPreference:_m.ReadPreference.NEAREST});

But it seems to be using a round-robin approach because setting secondaryAcceptableLatencyMS to 200 will cause my client to connect to servers on the otherside of the world. I thought that setting was just a gate, and then it connected based on min latency?