Chrome for iOS looks good - gets over 30 on our performance test - but it has a much slower javascript engine than Safari because apps aren't allowed to use JIT.
So it's something like this:
Safari: hardware accelerated, fast javascript
Chrome for iOS: hardware accelerated, slow javascript
PhoneGap: software rendered, slow javascript
Hardware acceleration is more important than javascript speed (Chrome is only a bit slower than Safari on iOS), so it's a good result. In short, Chrome is much better than PhoneGap, but not as good as Safari.