compare.rb

require 'benchmark/ips'

Benchmark.ips do |x|
  x.report("if") do |i|
    if i % 5 == 0
      i
    end
  end

  x.report("raise") do |i|
    begin
      raise unless i % 5 == 0
    rescue
      i
    end
  end

  x.compare!
end

result.txt

Warming up --------------------------------------                                          
                  if   319.284k i/100ms
               raise    69.463k i/100ms
Calculating -------------------------------------                                          
                  if    317.735B (± 6.4%) i/s -    831.988B                                
               raise     65.204B (±20.1%) i/s -    183.890B                                

Comparison:
                  if: 317735485266.5 i/s
               raise: 65203928436.3 i/s - 4.87x  slower