^
That's the most idiotic advice anyone can give. Playing the waiting game makes 0 sense as there will ALWAYS be something faster than what you have coming out later, or the same level of performance for much cheaper. You're almost always better off just getting the best you can afford at the time that you can afford it.
OP, you just need to make sure that the games you play most/are planning to play support SLi well enough, and if so, go SLI 980s as that will provide the most performance. However, if you are someone who prefers being able to run games at highest IQ settings (rather than highest possible FPS), you might want to get a 980Ti now and double up later as many new games can use 4+GB of vram at 2560x1440.