ExtJS: modx-combo-user and huge lists of users?

{
    xtype: MODx.config.publish_document ? 'modx-combo-user' : 'hidden'
    ,fieldLabel: _('resource_createdby')
    ,description: '<b>[[*createdby]]</b><br />'+_('resource_createdby_help')
    ,name: 'created_by'
    ,hiddenName: 'createdby'
    ,id: 'modx-resource-createdby'
    ,anchor: '100%'
    ,value: config.record.createdby || MODx.user.id
}

MODx.combo.User = function(config) {
    config = config || {};
    Ext.applyIf(config,{
        name: 'user'
        ,hiddenName: 'user'
        ,displayField: 'username'
        ,valueField: 'id'
        ,fields: ['username','id']
        ,pageSize: 20
        ,url: MODx.config.connector_url
        ,baseParams: {
            action: 'security/user/getlist'
        }
        ,typeAhead: true
        ,editable: true
    });
    MODx.combo.User.superclass.constructor.call(this,config);
};
Ext.extend(MODx.combo.User,MODx.combo.ComboBox);
Ext.reg('modx-combo-user',MODx.combo.User);

/* store the original onLoad method to have acces to it in the override */
var originalComboBoxOnLoad = Ext.form.ComboBox.prototype.onLoad;
/* fixes combobox value loading issue */
Ext.override(Ext.form.ComboBox, {
    loaded: false
    ,setValue: Ext.form.ComboBox.prototype.setValue.createSequence(function(v) {
        var a = this.store.find(this.valueField, v);
        if (v && v !== 0 && this.mode == 'remote' && a == -1 && !this.loaded) {
            var p = {};
            p[this.valueField] = v;
            this.loaded = true;
            this.store.load({
                scope: this
                ,params: p
                ,callback: function() {
                    this.setValue(v);
                    this.collapse()
                }
            })
        }
    })
    // this sets the width of combobox dropdown lists automatically to the width of the combobox element
    // and thus prevents the sometimes unnecessary wide dropdowns
    ,onLoad: function() {
        var ret = originalComboBoxOnLoad.apply(this,arguments);
        // true flag on getWidth() to ignore border and padding
        var maxwidth = Math.max(this.minListWidth || 0, this.wrap.getWidth(true));
        this.list.setWidth(maxwidth);
        return ret;
    }
});

$id = $this->getProperty('id');
if (!empty($id)) {
    $c->where(array(
        'id' => $id
    ));
}