If you need multiple locations within the US; you may want to look at i.e. Softlayer DC; they have datacenters in Dallas, Washington DC and Seattle ; which are also connected through a private network.
But depending on your needs there might be other solutions as well.
The speed the servers connect to each other depends on the datacenter your in and the quality of your connection. In general you can get very fast / high quality connections at good quality datacenters in the USA. As the poster above me mentioned some companies provide a private network connection between datacenters in multiple cities, which will cut down on your bandwidth costs etc.
There are hundereds of datacenters in the USA so just find a good quality one to ensure that you get a good connection.