Will the AMD R9 290X TRI X Fit into the ASUS M5A99X?



Considering the middle drive cage is removable, should be no problem. It will accept a card 320mm (12.6") in length with the cage removed. If you need to keep the middle drive cage in place, you'll need to find a card 270mm (10.63") or less in length.
 

Is there any other cases I can consider in that price range which will do the Job anyway? what's the use of the drive cage? Is that the HDD slots? if so I'm ony going to be using 1 HDD and SSD. along with 1 dvd drive, would all of this be fine?