To previous commentor is your xbox lying horizontal when you have the fan pointed at the hdd vent? Mine is freezing now and im getting the 2 red rings. But only on this game! Pretty frustrating but installing on a flash drive did help me to get to around 45%.
Yes, I have my Xbox lying horizontally. I think it is easier for my fan to blow onto the HDD side when it is laying flat. Previously I tried propping it up, but that didn't seem to make a difference (granted, that is when I was still blowing air on the back of the case).