Chicago Colo

The company i work for is growing at a rapid pace. We need to decide on if we want to colo or add better,bigger connection to our office.

We currently have DSL from Att 6/1 in downtown chicago.

Our product is a web app which people login and use. It runs in IIS, the user can see there data in various forms when the web server makes MS SQL query on the MS SQL that is also on the web server box which is 2u. The user can also download pdf report which range in size from 2meg to 30megs. Due to a limits of our dsl connection the more user's that use it the slower the end user's experience is due to the inet bottleneck. So our option is to get a T1 from ATT,covad or other provider or colo our server.

what factors should i take into account when looking at colo's in the chicago area. I am not sure how much b.w. this apps uses or any other factors the server would be a Dell 2950.