0) what about disabling all plugins and anebling it one-by-one to track the problem?

1) mayby it is better to limit resources for the Apache process and limit the time and resources for php scripts rather than killing Apache? Brute force kill -9 does not eliminate the cause, it only eliminate the results.

2) I had sped up a lot my wordpress simply by installing eAccelerator, very simple and effective. Time of generating a page is about 0.5 sec, before it could last even 30secs!

3) what can You see in (error) logs?

4) You can also try lighttpd insted of apache 😉