How should I upgrade?

I currently have an MSI Nvidia GTX 660 Ti OC edition. I can run most games on max settings but there are more and more games coming out nowadays that require me to drop to medium and in the case of the new assasin's creed unity I don't even meet the minimum requirement of a GTX 680. I know I need to upgrade soon, but i want to know if I should buy another GTX 660 Ti and do SLI or just get an all new beast card. Cheaper is better, but if there are any issues with sli or if its more bang for the buck to go single card I'd be willing to cough up a bit more. Also would the sli option allow me to run 98% of games at max or do I have to get a beast card to do that. I don't need to run crysis at max, but I do hope to run GTA 5 and similar games at max 60fps


Also if you need the info on my other components these are them.

-AMD FX 8350 8-core 4.0 GHz Black Edition


-240 GB SSD + 1TB HDD + 2TB HDD

SLI hasn't won me over yet, as it seems that it's still a little dodgy in some games as far as whether it improves performance or not. It's pretty much up to the developer, but not all are developing with SLI in mind still.

The main kicker that would prevent me from doing SLI if it were my decision would be the fact that putting 2 cards in SLI isn't going to increase your RAM. The 660 Ti with 2 GB is still decent at the moment but as newer games come out with higher and higher resolution textures, it will start filling up fast. 

At the moment you can get a 760 with moderately faster speed, and double the RAM, or even jump up to a 780 for about double the performance. Source

I actually didn't think of the comparability issues, and I should have considering I did the research for my CPU. (Still went with 8 core for video processing) Also My GTX 660 Ti is the 3GB model,

IF you can find another 3GB 660ti sli could work, but a 770 or better would probably be a better choice for you.

As far as I know SLI scales at about 1.7x performance. Also, good luck finding another 3gb version of your card online (ebay has none), you might be able to sell yours for 200-250 considering its rarity. That could give you a 970 for 100 bucks and basically double performance, and you wont have to worry about wether your PSU can handle it.

get a 970, i have g1 gaming edition and it easily maxes out any game