I really thought at the level of abstraction we typically work (Node.js) the idea of "write combining" wasn't going to make a difference. I was wrong.

test.js

//To understand how I started down this rabbit hole, go here: http://mechanical-sympathy.blogspot.com/2011/07/write-combining.html


var iterations = parseInt(2147483647 / 128);
//Base case, no optimization	
function runCaseOne () {
	console.time('caseOne');
	var i = iterations,
		arrayA = [],
		arrayB = [],
		arrayC = [],
		arrayD = [],
		arrayE = [],
		arrayF = [];
		
	while (--i > 0) {
		arrayA.push(1); 
		arrayB.push(1); 
		arrayC.push(1); 
		arrayD.push(1); 
		arrayE.push(1); 
		arrayF.push(1); 
	}
	console.timeEnd('caseOne');
}
//Write combining	
function runCaseTwo () {
	console.time('caseTwo');
	var i = iterations,
		arrayA = [],
		arrayB = [],
		arrayC = [],
		arrayD = [],
		arrayE = [],
		arrayF = [];
	while (--i > 0) {
		arrayA.push(1); 
		arrayB.push(1); 
		arrayC.push(1); 		
	}
	i = iterations;
	while (--i > 0) {
		arrayD.push(1); 
		arrayE.push(1); 
		arrayF.push(1); 
	}
	console.timeEnd('caseTwo');
}	
//Loop unrolling
function runCaseThree () {
	console.time('caseThree');
	var i = iterations,
		arrayA = [],
		arrayB = [],
		arrayC = [],
		arrayD = [],
		arrayE = [],
		arrayF = [];
	while (i > 0) {
		i = i - 4;
		arrayA.push(1); 
		arrayB.push(1); 
		arrayC.push(1); 		
		arrayD.push(1); 
		arrayE.push(1); 
		arrayF.push(1); 

		arrayA.push(1); 
		arrayB.push(1); 
		arrayC.push(1); 		
		arrayD.push(1); 
		arrayE.push(1); 
		arrayF.push(1); 

		arrayA.push(1); 
		arrayB.push(1); 
		arrayC.push(1); 		
		arrayD.push(1); 
		arrayE.push(1); 
		arrayF.push(1); 

		arrayA.push(1); 
		arrayB.push(1); 
		arrayC.push(1); 		
		arrayD.push(1); 
		arrayE.push(1); 
		arrayF.push(1); 


	}
	console.timeEnd('caseThree');
}
//Loop unrolled write combining?
function runCaseFour () {
	console.time('caseFour');
	var i = iterations,
		arrayA = [],
		arrayB = [],
		arrayC = [],
		arrayD = [],
		arrayE = [],
		arrayF = [];
	while (i > 0) {
		i = i - 4;
		arrayA.push(1); 
		arrayB.push(1); 
		arrayC.push(1); 		

		arrayA.push(1); 
		arrayB.push(1); 
		arrayC.push(1); 		

		arrayA.push(1); 
		arrayB.push(1); 
		arrayC.push(1); 		

		arrayA.push(1); 
		arrayB.push(1); 
		arrayC.push(1); 		

	}
	i = iterations;
	while (i > 0) {
		i = i - 4;
		arrayD.push(1); 
		arrayE.push(1); 
		arrayF.push(1); 

		arrayD.push(1); 
		arrayE.push(1); 
		arrayF.push(1); 

		arrayD.push(1); 
		arrayE.push(1); 
		arrayF.push(1); 

		arrayD.push(1); 
		arrayE.push(1); 
		arrayF.push(1); 

	}
	console.timeEnd('caseFour');
}
		
	
for (var i = 1; i <=3; i++) {
	runCaseOne();
	runCaseTwo();
	runCaseThree();
	runCaseFour();
}

kroberts-macpro:Desktop kroberts$ node looptest.js 
caseOne: 4668ms
caseTwo: 4169ms
caseThree: 4667ms
caseFour: 3538ms
caseOne: 4448ms
caseTwo: 3008ms
caseThree: 4271ms
caseFour: 3102ms
caseOne: 4287ms
caseTwo: 3243ms
caseThree: 4343ms
caseFour: 2834ms