Check out Ben Adams' benchmarks at https://github.com/benaadams/PeachpieBenchmarks

We haven't benchmarked WordPress yet, as we haven't even started doing any optimization work. It's faster than expected though, but we'll produce a proper benchmark soon.

They have benchmarks here: http://www.peachpie.io/benchmarks

The last one is probably the most useful and impressive.

As mentioned by sibling, not WP-specific, and benchmarks often lie, but better than nothing.