Originally Posted by epitome

Slow sites = memory upgrade...it's almost certain not to be the network unless you're using some two bit host.

As for processor, I don't know ... but my general rule of thumb is to double RAM one and then if your sites slow, upgrade to a better server. I don't even know if that's the right thing to do but it works great for me.

For the third question, I don't know ... but your sites should be fast.

Use webwait.com. If your site takes more than 3 seconds to load then it's too slow and you may be losing surfers. If you're running a blog and it's slow, kill plugins and it will drastically improve. I got a blog down from 7 to 2 by doing that. 3 seconds is the worst you want, try to keep it under 2 seconds. It it totally possible to get it under 1 second but you're typically not going to lose surfers if it's under 3.