What is the low down on these? Do you notice any difference in speed or anything?

Of course different servers run at different speeds. Do you mean by brand? No, brand affects reliability but generally when something is stated to run at a certain gigahertz it runs at it or very close to it.

Providing your server is setup and configured properly you should be able to outperform a shared hosting environment primarily because theres less to process however that would depend on who you get the shared hosting account with.

It would depend on what you are looking to get and what you are running.

Please clarify your question just a bit...