http://thr3a.hatenablog.com/entry/20151203/1449136273

bulk.rake

require 'benchmark'
namespace :bulk do
  desc "TODO"
  task insert: :environment do
    Task.delete_all
    Benchmark.bm 100 do |r|
      r.report "normal" do
        1000.times do |i|
          Task.create(title: "#{i}", content: "content #{i}")
        end
      end
      r.report "bulk" do
        tasks = []
        1000.times do |i|
          tasks << Task.new(title: "#{i}", content: "content #{i}")
        end
        Task.import tasks
      end
      r.report "without validate" do
        tasks = []
        1000.times do |i|
          tasks << Task.new(title: "#{i}", content: "content #{i}")
        end
        Task.import tasks, validate: false
      end
      r.report "without validate and new" do
        tasks = []
        1000.times do |i|
          tasks << ["#{i}", "content #{i}"]
        end
        Task.import ['title', 'content'], tasks, validate: false
      end
    end
  end
end

result.txt

mPro:hoge thr3a$ rake bulk:insert
                                                                                                           user     system      total        real
normal                                                                                                 1.360000   0.470000   1.830000 (  2.095945)
bulk                                                                                                   0.310000   0.010000   0.320000 (  0.317949)
without validate                                                                                       0.160000   0.000000   0.160000 (  0.168920)
without validate and new                                                                               0.080000   0.000000   0.080000 (  0.085750)