I have average cpu usage around 70% on my server, is that considered ok, or should I upgrade it? thanks.
it is ok and you better check load average. if the load average number is more than number of cores for a long time, your server is overloaded
It depends what you're worried about. Are you worried about pages slowing down? Or your server toppling over? Is your CPU throttling itself by putting itself into a sleep mode. If it is, you might want to force it to run at maximum speed all of the time.