I'm surprised that you didn't mention HipHop, especially if performance is your biggest gripe. It really is the bee's knees and will only get better.
I spent a good chunk of my day looking at PHP code and profiling data. Assocs are terrible for performance but it's not a fatal flaw IMO. What people really want are separate "vector", "dict" and "set" types. It also needs a decent standard library to replace dyslexic crap like explode(). And don't get me started on the string libraries and the abuse of preg_* functions.
Lastly, comparing plain PHP to Ruby+Rails isn't fair. I prefer Python myself but even then I need something like webpy or Google's appengine library to make reasonable app.
Show me a website where php is the source of the performance problems and I will show you a website php allowed to reach success/a large audience.
Frankly, unless you are very large scale php is never your bottlenecks, I/O is. And if php become your bottlenecks, you have already won.
(of course you could find exemples of math-heavy calculating sites where this isn't true, but that just means you don't know how to pick the right tool for the job)
You are right that I/O is usually the first bottleneck. I assure you that being CPU bound is no picnic, not least because most optimization knowledge and experience out there relates to I/O. :)
Even if you are not CPU bound, HipHop is steadily adding grown-up features to the language that make it quite nice to use, functions like mysql_connect_with_db() which save a database round-trip, and extensions like xhprof which will tell you what is actually slow.
If performance is a problem, then PHP is most certainly not the source of it, the vast majority of performance issues people are having in PHP are related to poorly written code, bad understanding of the language, and most of all use of third party software that were never meant to be performant(WordPress, SugarCRM, Symfony, ZendFramework ...).
And HipHop is most definitely not the solution, the only reason to use HipHop is if you are Facebook.
I spent a good chunk of my day looking at PHP code and profiling data. Assocs are terrible for performance but it's not a fatal flaw IMO. What people really want are separate "vector", "dict" and "set" types. It also needs a decent standard library to replace dyslexic crap like explode(). And don't get me started on the string libraries and the abuse of preg_* functions.
Lastly, comparing plain PHP to Ruby+Rails isn't fair. I prefer Python myself but even then I need something like webpy or Google's appengine library to make reasonable app.