Tak emy case for example, I COULD mount a dual sized rad in the top drive bay, but if I add a shroud and powerful fans, I am looking at loosing more drive bays than I am willing to part with, or doing away with a shroud and or thick fans. On the other hand, removing the frotn bottom hard drive rack, leaves me with 2 3.5 bays and 5 5.25 bays, and enough room in the bootm fron for a single sized rad. I currently have a shrouded BIX with an ultra panaflo on it. (Plan on putting a PA160 there soon as I can get one), and in the top rear I have fitted a BIM2 at the rear 80mm exuast ports. The bulk of the cooling is done by the BIX, however the BIM2 gives the extra oomph needed.
I woudl liek to have a single rad, just plain easier to work with tubing wise, but in my case I wasn't willing to part with the drive bays, and wiring layout I had planned. For instance, my inverters for the case lighting are hidden in the 3.5" bays. And my various leads for my wiring collect at teh point directly behind the 3.5" bays. If I had lost my 5.25 bays, I would have had to use thos bays to hold hard drives, and would have had a much more difficult time wiring the case, not to mention the situatioen of the rad woudl not have been ideal.