分かってはいたがまあやってみて、same-ish だった。

ternary_equal_notequal.rb

require 'benchmark/ips'

def ternary_equal
  (true == true) ? true : false
end

def ternary_not_equal
  (true != false) ? true : false
end

def if_equal
  if(true == true)
    true
  else
    false
  end
end

def if_not_equal
  if(true != false)
    true
  else
    false
  end
end

Benchmark.ips do |x|
  x.report('ternary_equal')   { ternary_equal }
  x.report('ternary_not_equal')   { ternary_not_equal }
  x.report('if_equal')   { if_equal }
  x.report('if_not_equal')   { if_not_equal }
  x.compare!
end

__END__

$ ruby ternary_equal_notequal.rb
Warming up --------------------------------------
       ternary_equal   192.244k i/100ms
   ternary_not_equal   133.545k i/100ms
            if_equal   125.349k i/100ms
        if_not_equal   151.554k i/100ms
Calculating -------------------------------------
       ternary_equal      5.941M (±21.3%) i/s -     28.260M in   5.028214s
   ternary_not_equal      4.658M (±20.0%) i/s -     22.168M in   5.024899s
            if_equal      5.467M (±20.5%) i/s -     25.822M in   5.028798s
        if_not_equal      3.616M (±26.6%) i/s -     16.065M in   5.009075s

Comparison:
       ternary_equal:  5941095.7 i/s
            if_equal:  5467124.3 i/s - same-ish: difference falls within error
   ternary_not_equal:  4657866.1 i/s - same-ish: difference falls within error
        if_not_equal:  3615514.5 i/s - 1.64x  slower

ruby tmp2.rb  24.16s user 0.25s system 84% cpu 28.943 total