This is true and the results are commendable, though honestly I believe that the only reason that Zend upped their game was because competition from Facebook's efforts lit a fire under their ass.

indeed. for some comparison just betwwen php 5.4, 5.5, 5.6, 7, and HHVM, view some benchmark results in recent PHP talks...

http://talks.php.net/singapore15#/drupalbench

php7 is sometimes faster than hhvm, and sometimes a bit slower, but both are generally faster to much faster than earlier versions.

(and 5.4 was faster than 5.2 which the GP referenced)