My company web site uses a lot of AJAX, what should I be looking for in choosing a great dedicated server for a very fast performance?

I’m looking a GOOD dedicated server for my company which will give the company web site great performance. Unfortunately, storaging on another server with more web sites gave very weak performance.

The site is using a lot of AJAX, like fluther.com does, so I will be glad for advise what is the most important thing I should look for in dedicated server: Ram or CPU or something else?

Where Fluther.com hosting their web site? If it is not a secret.

Please advise.