Dody what kinda sites you running (pm me?) I host large forums currently, it's a semi dedicated setup where each site feeds off the same servers, but their's multiple servers. So we got webservers php-fastcgi servers mysql servers memcache servers... In the event a site is large enough we can give them their own dedicated php server for example or mysql server, yet share on the same webserver.
Why do you need a control panel based server? Go with a LAMP and the performance will be much better. Fine tune and optimize services, think about caching etc and you will do fine with 100.000 daily hits. We have sites doing millions of hits daily on a single HW. However, if you need high uptime etc, you will need to do load balancing with multiple servers - kernel upgrades etc won't bring down your site.