buffer-access-benchmark.js

var Benchmark = require('benchmark');
var suite = new Benchmark.Suite;

global.minOps = 1024;
global.undersized = new Buffer(3);
global.exactSize = new Buffer(global.minOps);

function access(buff, size) {
	for (var i = 0; i < size; i++) {
		buff[i];
	}
}

suite
	.add("undersized  ", function () {
		access(global.undersized, global.minOps);
	})
	.add("exact length", function () {
		access(global.exactSize, global.minOps);
	})
	.on('cycle', function(event) {
		console.log(String(event.target));
	})
	.on('complete', function() {
		console.log('Fastest is ' + this.filter('fastest').pluck('name'));
	})
	.run();

My result:

$ node buffer-access-benchmark.js 
undersized   x 7,304 ops/sec ±0.84% (97 runs sampled)
exact length x 4,597 ops/sec ±0.70% (100 runs sampled)
Fastest is undersized  

$ node --version
v4.1.1