Given that I don't think PHP (or HHVM) developers have been testing their PHP performance against PTS, it should be for some interesting untested grounds. The PHP benchmarks I've been doing, of course, have been of the Phoronix Test Suite itself. In developing PHPNG/PHP7, the developers were reportedly using WordPress performance as their benchmark for gauging performance. There's many benchmarks out there already showing that for Apache and other popular web frameworks and content management systems there is indeed great performance gains up to around 2x for PHP 7 compared to PHP 5. On the language side, PHP 7 will allow for declaring return types, scaler type hints, a combined comparison operator, a null coalescing operator, and other features. Optimizations to internal data structures should not only yield better performance results but greater memory savings too. Zend Engine 3 utilizes an AST-based compilation process, but still isn't a JIT compiler like HHVM. PHP 7's Zend Engine has been significantly refactored while retaining compatibility with PHP 5's language syntax.
PHP 7 in many cases has been advertised as being "2x faster" than PHP5 due to the significant strides made on "PHPNG" experimental code branch. Here are some benchmarks I did on Ubuntu Linux x86_64 comparing the performance of PHP 7.0 RC2 to PHP 5.3/5.4/5.5/5.6, along with some HHVM results tossed in at the end. To the say the least, the performance claims made by PHP developers about the upcoming PHP7 release are very accurate: it's pretty darn fast and about twice as fast as PHP 5.6.
With PHP 7.0 RC2 having just been released, I've been testing it out thoroughly across a range of Linux systems at Phoronix.