I personally run my Challenger with an additional side intake fan. I have found it is best to keep the three originals as they are and add one 120mm fan intake on the door panel.
Note that the door panel has mounts for 80mm, 90mm and 120mm fans - your top exhaust fan is 140mm and won't fit on the door straight - you might be able to mount it crooked using the air holes though. Throwing a fan like this on there will help (and isn't too expensive) http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Hope it helps
Fans are inexpensive. Add one to the side panel unless you don't want the extra noise. In that case, move either of the top fans to the side. If your cooler is stock, I'd remove the rear fan to the side. If the cooler is aftermarket, leave in place whichever fan is in the direction of the cooler airflow to help exhaust the heated air from the case.
Hmm, I didn't realize that the top exhaust for the Challenger was 140mm. I guess it'd be in my best interest to get another 120mm, then. I haven't bought case fans before, though. Any advice? There seem to be a lot of bearing types, as well as airflow vs. pressure. What are the differences?
Case fans are an accessory that come in every flavor and color of the rainbow, with all the options, prices can get steep. The primary differences in fan functions are airflow, static pressure and noise. The type of bearings used seem to have more to do with the life expectancy of the fan than the fan's ability to move air. I have amassed quite the collection of fans over the years - I can't say which is best.
One thing to note about door mounting on the Challenger with a full size graphics card in place - you are limited to a fan 25mm thick (which is the "standard") - you have about 30mm clearance between the door and your graphics card. Another consideration in fans is how you want to plug it in. Some fans will have a molex connector (goes straight to the PSU - cannot adjust speed), others have the 3pin fan connectors and can connect straight to the motherboard (and speed can be controlled if the motherboard supports it) a few have both.