It doesn't make much sense actually. Comparing Peachpie-powered PHP5 and PHP7 doesn't have all that much value. With that said we are going to do it anyway in the next week or so, but we expect PHP7 to be faster. The real value comes from comparing PHP7 with Peachpie-powered PHP7.
The language changes that happened in PHP 7 are, with maybe two exceptions (func_get_args and foreach details) not related to performance. So if you're comparing performance (and not language support), there is nothing wrong with comparing a Peachpie PHP5 implementation to a Zend PHP7 implementation. The Zend implementation does not derive any significant benefit from being PHP7 compliant (as far as performance is concerned).
Well. PHP 7 has a completely reworked opcode cache and many other tweaks that increase its performance across pretty much all applications tested (including the Zend framework itself according to Zend). With that said, however, as we mentioned earlier, we will not shy away from the comparison. We are working towards a performance benchmark that will compare Peachpie and PHP 7. But as we haven't focused on performance optimization yet at all, we don't expect Peachpie to outdo PHP 7 quite yet. Give us a few days/weeks and we'll publish the first benchmarks. We're curious as well :)