Also, the Ultra has better benchmarks on every site and the dual slot exaust allows the hot air to escape from the back of your computer. The GTX might take up another slot inside your case, but with no exaust its going to get pretty hot.
Note for BOTH cards... Note: This card is 275mm in length so make sure it fits in your case! Also the cards require PCI-E x16 slots, they will not function in a x8 slot so for SLi you need dual x16 mainboard. Finally 500W minimum for PSU and 600W+ is recommended.