Yes, I also read about phpsuexec causing security problems, hence I did not use it until now. I have a problem with httpd running in excess of 90mb. It was suggested by someone that I enable phpsuexec to track the problem. After enabling phpsuexec, I still couldn't track the problem. So, I will be turning it off later.
I am assuming that you don't just have too many sites hosted on your server ...
The first thing I would do before anything else on that is go to "View Bandwidth Usage"
and sort the sites on your server by bandwidth usage because I'd be willing to bet that
the excess usage is going to fall out of one of the first few on the top of that list.
The next thing would be to actually look at the cooresponding log files located in
/etc/httpd/domlogs and see what is actually going on for those sites.
While in that directory, you could also do an "ls -lSr | tail" and see what sites have
the largest log files and examine those files to see what is going on.
Excessively large log files will definitely contribute to high resource load levels for
Apache especially if the error_log file grows too large. It is generally a good idea
to roll the logs when the statistics update daily. Likewise, I would check the general
logs in /etc/httpd/logs and make sure the error_log and access_log files have not grown
excessively too large. I've seen some greater than a gigabyte on some servers!
Meanwhile you can also do a few "Apache Status" views when you are noting the higher
loads and that will tell you what is happening with Apache at that precise moment.
Multimedia streaming such as video or audio, large file upload or downloads, or
poorly written CGI scripts (usually Perl) are the usual typical culprits behind
higher usage loads so keep a keen eye out for that when reviewing log files and
Apache status screens, etc.
Another one that people don't often think about is hotlinked images. Take a simple
signature image and place it on a few popular forum sites hotlinked to a site on your
server and you could be getting more simultaneous connections for that small file
than your server can handle in the period of time between requests.
Hope that helps!
PS: Using phpSuExec would actually INCREASE your Apache memory usage! LOL