I just took my 304 apart. It sits on a desk and our house is dusty and I just demo'd our kitchen. First time opening a case after 6 months and no dust bunnies. Very light dust around the front fans, didn't even need to wipe the video card fans down. This is for a gaming PC, 2 SSD's and 1 7200rpm drive, 4770k, AMD 7850 and the inside was pretty warm. The little fans up front may blow air in through the drives, but I really don't think this case would be good for 6 drives. Its almost time to swap the 7200 drive with an SSD, as I am sure that will fail shortly.
I am sure you can find a slightly larger case that handles spinning drives much better. As to my TS140, I wish I ended up going with something with more expansion for down the road. You can never have too much space!