Benchmark to see if ActiveRecord::Base.include_root_in_json significantly affects performance

bm.rb

# encoding: utf-8

require 'benchmark'
require 'json'

json_normal = <<-EOS
[
  {
    "order": {
      "checkin_id": 298486374,
      "created_at": "2011-08-18T19:48:57Z",
      "id": 298486374,
      "read": null,
      "status": "pending",
      "store_id": 800752302,
      "table_id": null,
      "updated_at": "2011-08-18T19:48:57Z",
      "user_id": null,
      "selections": [
        {
          "id": 298486374,
          "note": null,
          "selected_options": null,
          "product": {
            "description": "Is it a copyright violation to use McDonalds on my test file? I hope they sue me.",
            "id": 699613630,
            "name": "Big Mac",
            "price": "€3.40"
          }
        }
      ]
    }
  },
  {
    "order": {
      "checkin_id": 980190962,
      "created_at": "2011-08-18T19:48:57Z",
      "id": 980190962,
      "read": null,
      "status": "pending",
      "store_id": 800752302,
      "table_id": null,
      "updated_at": "2011-08-18T19:48:57Z",
      "user_id": null,
      "selections": [
        {
          "id": 980190962,
          "note": null,
          "selected_options": {
            "Dessert": "Sundae",
            "Sauce": "Extra hot"
          },
          "product": {
            "description": "A delicious cheasy greasy pie",
            "id": 266175090,
            "name": "Pepperoni Pizza",
            "price": "€10.99"
          }
        }
      ]
    }
  }
]
EOS

json_rootless = <<-EOS
[
  {
    "checkin_id": 298486374,
    "created_at": "2011-08-18T19:48:57Z",
    "id": 298486374,
    "read": null,
    "status": "pending",
    "store_id": 800752302,
    "table_id": null,
    "updated_at": "2011-08-18T19:48:57Z",
    "user_id": null,
    "type": "order",
    "selections": [
      {
        "id": 298486374,
        "note": null,
        "selected_options": null,
        "product": {
          "description": "Is it a copyright violation to use McDonalds on my test file? I hope they sue me.",
          "id": 699613630,
          "name": "Big Mac",
          "price": "€3.40"
        }
      }
    ]
  },
  {
    "checkin_id": 980190962,
    "created_at": "2011-08-18T19:48:57Z",
    "id": 980190962,
    "read": null,
    "status": "pending",
    "store_id": 800752302,
    "table_id": null,
    "updated_at": "2011-08-18T19:48:57Z",
    "user_id": null,
    "type": "order",
    "selections": [
      {
        "id": 980190962,
        "note": null,
        "selected_options": {
          "Dessert": "Sundae",
          "Sauce": "Extra hot"
        },
        "product": {
          "description": "A delicious cheasy greasy pie",
          "id": 266175090,
          "name": "Pepperoni Pizza",
          "price": "€10.99"
        }
      }
    ]
  }
]
EOS

n = 100_000
Benchmark.bm(8) do |x|
  x.report('normal')   { n.times { JSON.parse(json_normal) } }
  x.report('rootless') { n.times { JSON.parse(json_rootless) } }
end