You don't seem to understand the core at play here. Just because the card has X amount of memory doesn't mean it'll perform better.
You also have to factor in cost vs. performance. E.g. my old GTX760 m-ITX version ran BF4 @ 1080p on high without issues (with an i5 4670 and 8GB of DDR3 RAM).
ATi cards tend to be overpriced because of their mining ability.
Most boards can't handle 2x 16xPCIe-3, they default to 8x/8x or worse, so the performance gain from SLi/Crossfire isn't that great (unless you picked up the second car for really cheap).
GTX960 are around the $300 mark. Since you're going to spend $400+, might as well $500 on a GTX970, which will poo all over the 290.
Main point is, set your budget. I used to be an AMD fan but they've dropped the ball and Intel/nvidia have really pulled away (especially with the thermal usage).
Feel free to search for benchmarks/review/builds, research is key. Here's a couple to start you off with:
http://www.videocardbenchmark.net/high_end_gpus.html
https://www.cpubenchmark.net/high_end_cpus.html