Depends. If your HDD shelf gets in the way, 9 inches to be sure, if the shelf is wide enough not to get in the way - 4 should be more than enough. (The measures are from my ATX case, as your is an ATX one too I suppose from the photos).
Although I doubt that the HDD shelf could be wide enough as the HDD format is the same..
Edit: I may have exaggerated a little bit. I've just measured a free space for my GPU and it's about 9.8 inches. Supposing that your case should be the same format, I believe that both of the mentioned GPUs would fit.