Get yourself a high end virtual account with a respectable company. With your requirements you'd be an idiot to go dedicated. Know what you're getting yourself into or you'll end up with more downtime than you're having with your current host...
zxc, I totally agree with you -- I have a LOT of downtime on my shared servers . The only good thing about shared servers is that they are managed -- someone will reboot them when needed, install patches, monitor ports, fix things etc.
That's why I still keep my 8 sites on shared servers . I have no experience managing dedicated servers, and can't afford to pay extra $200-400 for a "management".
Should I move from a shared hosting to an unmanaged/semi-managed dedicated CPanel/WHM server if I don't have good experience with Linux?
>Should I move from a shared hosting to an unmanaged/semi-managed dedicated CPanel/WHM server if I don't have good experience with Linux?
this entirely depends upon your capability of quick learning. When I got my dedicated (TOTALLY unmanaged - at RS ) I did not know even a single Linux command. But within a week I without somebody's help upgraded CP, installed MRTG, Webalizer, firewall, etc. And for almost a month I did not expirienced any downtime except of 1 minute for one reboot. You can find at their forums detailed step-by-step instructions for absolutely any kind of operations need for managing dedicated server.
If you learn fastly, don't hesitate and sign-up for a dedicated right now.