I would like to get some feedback regarding a few single speed rigs I am look at. I want to use them primarily for some single track use here in Northern Illinois and Southern Wisconsin. In addition, I will use them as a commuter on occasion, especially in poor weather. They are a mix of 26" and 29" tires. I am looking for a steel frame, disc brakes (or at least the option to add them to the fork), possible fender and rack mount tabs, and single speed drivetrain. $600 is my max. Used or new is fine.

So here is the list:
Dawes Bullseye
GT Peace her
Redline Monocog
Nashbar Single Speed
Surly 1X1 (probably would be used)
Surly Karate Monkey (probably would be used)
Convert old Stumpjumper or Rockhopper (or similar)

Thanks.