I replaced Apache with Nginx and PHP-FPM due to the fact we ran into some memory overflow problems and httpd services crashed and the whole server needed a physical restart. I ran both Apache and PHP in the same resource and not separate as right know. So can't be 100% sure if were just mod_php or apache itself.
Haven't had a single crash now, so I'm going Nginx all the way now. And we can also handle a higher load (PHP-FPM will handle more than mod_php too).