Go with MPM Worker and configure it properly,
it improve performance about 30%
increasing the values won't speedup your websites and tune your servers.
also install memcache on the server via easyapache.
How to install MPM worker?
easily via easyapache,just uncheck mpm prefork and check mpm worker option on extended apache modules list.
as It's a webhosting server I'd recommend you to install cloudlinux to provide better quality and stability.
don't forget about tuning the mysql,it helps to decrease the server load and make it faster!