String concat speed.

Results

       user     system      total        real
   0.050000   0.000000   0.050000 (  0.043481)
   0.100000   0.010000   0.110000 (  0.107440)
   0.060000   0.000000   0.060000 (  0.062976)

Test

require 'benchmark'

first_name, last_name, x = 'Hugh', 'Evans', 100000

Benchmark.bm do |b|
  b.report { x.times { "#{first_name} #{last_name}" }}
  b.report { x.times { [first_name, last_name].join(' ') }}
  b.report { x.times { first_name + ' ' + last_name }}
end