I have a few points I would like to make first.
Servermatrix is a stand up company. They provide a good network with awesome reliability. They make money off of "additional" charges like special installs or custom requests. So if you need them to do something they will charge you $75/hr and want 1 to 3 hours to do it.
Cogent bandwidth is budget bandwidth. In the early days of the net all the "resellers" greatly oversold this to make serious coin. Couple this with routing hardware and protocols constantly being refined caused great strain on the Cogent infastructure. And resulted in down time and heavy packet loss. With new GigE connections and router protocol and hardware it has changed.
I personally don't use any Cogent network in my dealings but have noticed when servicing my clients who are on a Cogent network now.
THIS HAS CHANGED. It is almost like night and day on the Cogent network now. Still seeing some slow traceroutes but not to bad. Would not recommend it for game servers or streaming but for file serving I might consider it.
Note: I currently use Voxel.net's
http://www.voxrox.com and love it! Duel Opteron is amazing!!!!