First, 4GB of HBM with AMDs memory management has been proven to not be a bottleneck in any game. This includes all of the games that will load 6 to 8 GB if they have it available. Loading and using are two different things. Frankly, you are about a year behind in a discussion that has already be settled. Feel free to dig up the threads to catch up.
Second, we aren't talking about Fury X v 980Ti. All of the cheapest 980Tis on Newegg are reference cards and who wants one of those for overclocking? It's going to turn into a hot, loud card.
Third, all of the 980Tis on Newegg are $629 or higher. On top of that, you assume that just because you have $500 you have $600 when that isn't even remotely a logical assumption. Even if you have $600 you many not even want to spend $600. The Fury X is 5-10% ahead on average, but you have to spend $150 more. The 980 Ti is only 5% ahead of the Fury X if at all. Below is the latest card card to be reviewed. Notice how the Fury without this recent discount is still a better price to performance deal than the Fury X and the 980 Ti reference? Ya....
http://www.techpowerup.com/reviews/Zotac/GeForce_GTX_980_Ti_Amp_Extreme/25.html