Apex Performance - String Concat with XML vs ADD

// Test Config
String strX = 'value';
Integer itr = 100000;

/**
 * METHOD 01 Simple String Concat
 * Heap Size 24, CPU Time 5803 (100k iterations)
 */
// Add values to the simpleConcatString string
Integer heapStart = limits.getHeapSize();
Integer cpuStart  = limits.getCpuTime();
basicConcatMethod('');
Integer cpuEnd  = limits.getCpuTime();
Integer heapEnd = limits.getHeapSize();


/**
 * METHOD 02 XML StreamWriter Concat Method Cheat 
 * Heap Size 24, CPU Time 721 (100k iterations)
 */
Integer heapCheatStart = limits.getHeapSize();
Integer cpuCheatStart  = limits.getCpuTime();
xmlCheatMethod(new XmlStreamWriter());
Integer cpuCheatEnd    = limits.getCpuTime();
Integer heapCheatEnd   = limits.getHeapSize();

// Let's run it again with an example usage and also validate the results are the same
Assert.areEqual(
	basicConcatMethod(''),
    xmlCheatMethod(new XmlStreamWriter())
);

// Add the debugs at the end as we have a huge debug log with 100k iterations
System.debug('');
System.debug('HEAP string concat: ' + (heapEnd      - heapStart      ));
System.debug('CPUT string concat: ' + (cpuEnd       - cpuStart       ));
System.debug('');
System.debug('HEAP XML Cheat:     ' + (heapCheatEnd - heapCheatStart ));
System.debug('CPUT XML Cheat:     ' + (cpuCheatEnd  - cpuCheatStart  ));
System.debug('');


/**
 * Put your concatenation logic in here
 */
static String basicConcatMethod(String input){
    for(Integer i =0; i<itr; i++){
        input+=strX;
    }
    return input;
}


/**
 * or here
 */
static String xmlCheatMethod(XmlStreamWriter xsw){
    for(Integer i =0; i<itr; i++){
        xsw.writeCharacters(strX);
    }
    return xsw.getXmlString();
}