compare.rb

require 'benchmark/ips'

collection = 100.times.map { rand(10) }

TABLE = {
  6 => true,
  7 => true,
  8 => true,
  9 => true,
  11 => true
}

Benchmark.ips do |x|
  x.report "Fixnum#compare" do
    collection.each do |c|
      (c >= 6 && c <= 9) || c == 11
    end
  end

  x.report "hash lookup" do
    collection.each do |c|
      TABLE.key?(c)
    end
  end

  x.report "two whens" do
    collection.each do |c|
      case c
      when 6, 7, 8, 9, 11
        true
      else
        false
      end
    end
  end

  x.report "multiple whens" do
    collection.each do |c|
      case c
      when 6
        true
      when 7
        true
      when 8
        true
      when 9
        true
      when 11
        true
      else
        false
      end
    end
  end

  x.compare!
end

out

Warming up --------------------------------------
      Fixnum#compare    12.370k i/100ms
         hash lookup    12.527k i/100ms
           two whens    16.199k i/100ms
      multiple whens    15.754k i/100ms
Calculating -------------------------------------
      Fixnum#compare    152.121k (± 9.0%) i/s -    754.570k in   5.005868s
         hash lookup    129.428k (± 6.6%) i/s -    651.404k in   5.057921s
           two whens    130.044k (±25.9%) i/s -    599.363k in   5.017069s
      multiple whens    151.871k (±11.9%) i/s -    756.192k in   5.060006s

Comparison:
      Fixnum#compare:   152121.5 i/s
      multiple whens:   151870.7 i/s - same-ish: difference falls within error
           two whens:   130043.5 i/s - same-ish: difference falls within error
         hash lookup:   129427.9 i/s - 1.18x  slower