It's not the servers... (Score 2, Informative)

Check the load on the servers... that's not your problem. Check your bandwidth pipe. That is your bottle neck. Now just because you might have a 20 MB pipe doesn't mean you have 20 MB to the Internet. Bandwidth providers are famous for overselling pipes... that's how they make money! What you need to look into is getting a second ISP that feeds from a different data center than the one you have now. Now another option is to co-locate to a center that has multiple ISP feeds and place a publishing server at that location. Therefore you only use the bandwidth at your current site to send the feed to the co-location. They will most likely have three to four ISP feeds to the Internet and the cost is a lot less than adding more bandwidth and edge network services. With you being a non-profit you've got to have some leeway to get a better pricing deal.