Most of the optimizations listed can be found in the "Other Oddments" chapter of the Camel in the section "Efficiency". But one of my favorites (also in the Camel, but paraphrased using $x/$y/$z instead of $a/$b/$c):

Use  $foo = $x || $y || $z;  This is much faster (and shorter to say) 
+than:

   if ($x) {
      $foo = $x;
   } elsif ($y) {
      $foo = $y; 
   } elsif ($z) {
      $foo = $z;
   }
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--Jim