The following script only generates an array and walks through it with 2 different loops.
There are some strange effects while watching the durations of the loops.

1. Sometimes loop 1 is faster
1. Sometimes loop 2 is faster
1. Sometimes there is a negativ duration ... ?

PHP seems to behave in real bizarre way ... looks like it has a will of it's own ;-)

<?
function test()
{
 for ($i=0;$i<30000;$i++)
 {
  $GLOBALS['myVar'][$i]=$i;
 }
 $a = microtime();
 for ($i=0;$i<count($GLOBALS['myVar']);$i++)
 {
  $GLOBALS['myVar'][$i] = $GLOBALS['myVar'][$i] *2;
 }
 $b = microtime();
 foreach($GLOBALS['myVar'] as $i => $d)
 {
  $GLOBALS['myVar'][$i] = $d * 2;
 }
 $c = microtime();
 echo('Results ... <br>');
 echo("<b>$a<br>$b<br>$c</b><br>");
 list($m,$s)=explode(' ',$a);$a = doubleval($s)+doubleval($m);
 list($m,$s)=explode(' ',$b);$b = doubleval($s)+doubleval($m);
 list($m,$s)=explode(' ',$c);$c = doubleval($s)+doubleval($m);

 echo("<b>$a | $b | $c</b><br><br>");

 echo("Loop 1: ".($b-$a)." seconds<br>");
 echo("Loop 2: ".($c-$b)." seconds<br>");
 echo("<hr>");
}
test();test();test();test();test();
?>