I attempted to take some photos at a soccer game today. I used a Sigma 70-200 f2.8 APO HSM lens on the Canon 10D. I also used the Sigma 2X teleconverter which took the Aperture to 5.6. I was shotting in aperture priority mode. ISO 100. The shutter speed was coming out at about 1/125th. From the look of the shots(faces and body somewhat sharp, moving parts blurred) I need a faster shutter speed. What would be a good shutter speed to be shooting at to stop the action on this type of shot? How much shutter speed do I pick up by going to ISO 400 or say 800? Thanks in advance for the help on this.