That question depends on what your trying to accomplish.

If you're operating on a massive enterprise scale, it's probably not going to be good enough for your hardware. The HipHop VM might be a saving grace if you're already built on PHP, but pragmatically it's probably a better idea to choose a more matured solution (probably something on the JVM).

If you're doing something that is algorithmically intensive (video encoding as an arbitrary example) PHP is going to be a bad fit.

However, if you, like the vast majority of developers, are working on a website that's main technical purpose is to store data of some sort to a back end and retrieve it later for display and you're not yet operating on a large scale (1M+ users) then PHP itself is probably not going to be your bottleneck for a long time.

If you're a fan of benchmarking, techempower does a good job of unbiased comparisons (although keep in mind these are just benchmarks. It doesn't account for how a particular language or framework is optimized for): http://www.techempower.com/benchmarks/

Performance isn't bad. You've been able to install an opcode cache for years, and there's one built into the runtime now. HHVM really boosts performance, and it's closing in on full compatibility with mainstream PHP.

The most problem application is IO speed. While testing php speed,problem speed occur on include,require file.Each include toll 200 to 300 ms. If you build your server with SSD .It cut short the io issue.Don't overlook some micro optimization tips..