Sry, I have to bump this.
Iam having exactly the same problem. Using Steam C2 Personal, R173. On two different machines.
First: Win 7 64bit
Second: Win Vista 32Bit
C2 is slowing down until it gets temporarily stuck. I have to minimize C2 via task bar, maximize, minimize and so on, until C2 finally reaches its normal state. Sometimes, while using the Image Editor, it is not possible to restore C2s normal state. Forcing me to close the Application and lose every progress I have done so far.
Maybe it`s just subjective, but I think running Steam in offline mode reduces this "stuck" time to a minimum. Also I disabled the "cache icons in editor for better performance" option in combination with Steam in offline mode. Disabling this option while running Steam in online mode did reduce the hang time in my opinion. But again, this is just a subjective feeling. Those hangs could take around 2-4 seconds or 3-5 minutes until I can restore the application via minimize and maximize.
Those hangs are just affecting the C2 Application. RAM and CPU performace is quite normal.
Iam using C2 since around a year and Iam not able to tell exactly when this happend the first time. I did some small applications before. Data Visualization and small usability tests for academic studies with a maximum of 100 events with no problems. My current game project has around 690 events and in comparison to these other projects a lot of different graphics. And Iam having the feeling it does get worse while the project is growing.
While having a complete freez the task manager is showing 4 other C2 Applications in the Application Tab but just one C2 process in the process tab.
Also Iam getting a error dialog, saying something like "a required resource..." but nothing like "could not be found". It seems like there is missing another line in this dialog window.
Another thing, it`s not possible to start C2 via short cut or *.exe while Steam is in offline mode. Steam will tell you it`s not possible to run this game in offline mode. You have to start C2 via Steam.