php > $blah="blah"; $s=microtime(true); for($i=0;$i<100000;$i++) "omgwtf$blah\n"; echo microtime(true)-$s;
0.044615983963013
php > $blah="blah"; $s=microtime(true); for($i=0;$i<100000;$i++) 'omgwtf'.$blah."\n"; echo microtime(true)-$s;
0.042807102203369