in my judgment if you have 2 GTX 960's in SLI it is slightly better than a GTX 970 when you are preforming at a higher resolution than at 1080p. Also a lot of your posts talk about the limited 2 GB's VRAM. However if you look at the EVGA 960 FTW you can get 4 GB's worth of ram however the 128 bit bus is slow it still can out preform a 970 at 1440p gaming, however you will lose to a 970 at or below 1080p gaming.
So my conclusion is if you are planning to game at 1080p than there is no need to over pay and SLI 2 GTX 960's. However if you are playing at 1080p than that doesn't mean that you have to have a GTX 970 either. A GTX 960 one of the EVGA ones that sport a 4 GB buffer is more than enough to handle almost any game at 1080p. However for upgradeability you should really be thinking about get the 970. Remember you can add another one latter and be able to do some gaming at 4K. Just remember if you HAVE to run SLI GTX 960's that you have no upgrade room and that you will be limited to what the card has to offer. With a SLI of GTX 960's you will be paying more than a 970, and will be about only 100 dollars off from a GTX 980. Which is almost as good as a SLI of 970's.
This is my ideas about this card it is up for debate.