es6 arrow functions vs regular functions

bench.js

'use strict';

var callarrow = () => { return 1 };
var arrow = () => {
    var j = 0;

    for (var i = 0; i < 100; i++) {
        j += callarrow();
    }

    return j;
}

var callregular = function() { return 1 };
function regular() {
    var j = 0;

    for (var i = 0; i < 100; i++) {
        j += callregular();
    }

    return j;
}

function benchmark(n, f) {
  var start = process.hrtime();
  for (var i = 0; i < n; i++) f();
  var end = process.hrtime(start);
  
  console.log("%s took %s ns / op", (f.name || 'function'), ((end[0] * 1e9) + end[1]) / n);
}

benchmark(10000 * 10000, arrow);
benchmark(10000 * 10000, regular);

my results.txt

$ node
> process.version
'v4.0.0'
> process.versions.v8
'4.5.103.30'
$ node benchmark/functions
function took 145.01693226 ns / op
regular took 148.5491975 ns / op
$ node benchmark/functions
function took 144.78813348 ns / op
regular took 150.01348607 ns / op
$ node benchmark/functions
function took 147.5060453 ns / op
regular took 150.76537589 ns / op
$ node benchmark/functions
function took 147.22545045 ns / op
regular took 150.65283979 ns / op
$ node benchmark/functions
function took 146.93254574 ns / op
regular took 152.10227278 ns / op

I wonder if all these function calls don't just get optimized away...