You will need several to get the best out of them.
If you are not going to max the settings to use all the VRAM you can, a GTX 980 would be near enough as good as a single next gen Titan.
SlI is on my mind, and also the 980. But I am scare to get the 980 and then...pum! Nvidia put on sale the new Titan. I would kill myself.
