RSSライブラリーでREXMLを使う時とNokogiriを使う時のベンチマーク ref: http://qiita.com/items/ab872c13d2cf40fc572a

file0.rb

require 'benchmark'
require 'open-uri'
require 'rss'
require 'rss/nokogiri'

uri = 'http://ja.wikipedia.org/w/index.php?title=%E7%89%B9%E5%88%A5:%E6%9C%80%E8%BF%91%E3%81%AE%E6%9B%B4%E6%96%B0&feed=atom'
xml = open(uri) {|f| f.read}

Benchmark.bmbm do |x|
  x.report 'REXML from URI' do
    uri = URI('http://ja.wikipedia.org/w/index.php?title=%E7%89%B9%E5%88%A5:%E6%9C%80%E8%BF%91%E3%81%AE%E6%9B%B4%E6%96%B0&feed=atom')
    RSS::Parser.parse open(uri), true, true, RSS::REXMLParser
  end
  x.report 'Nokogiri from URI' do
    uri = URI('http://ja.wikipedia.org/w/index.php?title=%E7%89%B9%E5%88%A5:%E6%9C%80%E8%BF%91%E3%81%AE%E6%9B%B4%E6%96%B0&feed=atom')
    RSS::Parser.parse open(uri), true, true, RSS::NokogiriParser
  end
  x.report 'REXML from memory' do
    RSS::Parser.parse xml, true, true, RSS::REXMLParser
  end
  x.report 'Nokogiri from memory' do
    RSS::Parser.parse xml, true, true, RSS::NokogiriParser
  end
end

file1.txt

Rehearsal --------------------------------------------------------
REXML from URI         0.550000   0.000000   0.550000 (  2.712987)
Nokogiri from URI      0.170000   0.000000   0.170000 (  3.078010)
REXML from memory      0.540000   0.000000   0.540000 (  0.544707)
Nokogiri from memory   0.120000   0.000000   0.120000 (  0.122050)
----------------------------------------------- total: 1.380000sec

                           user     system      total        real
REXML from URI         0.560000   0.020000   0.580000 (  2.653760)
Nokogiri from URI      0.180000   0.000000   0.180000 (  3.760438)
REXML from memory      0.530000   0.000000   0.530000 (  0.534338)
Nokogiri from memory   0.100000   0.000000   0.100000 (  0.102664)