Gtx 770's are still boss. I have 2 Windforce GTX770 4gb cards. I love them.. in a "feels good in the pants," kinda way. 200 bucks is a steal!
Here is the thing about SLI. It all comes down to the publisher and what graphics engine they use. Look at Wolfenstein: New Order. A great looking game made on an outdated graphics engine by a reputable publisher (Bethesda). This game doesn't need SLI. It can be run by a single card on max graphics. So why would they make a SLI profile for it. Then there is Watch Dogs. Ubisoft doesn't make games for PC. They may sell them for PC but only because it is an extra source of revanue. They dont give a crap about PC optimization. So you can count on their games running like crap on PC. EA games like Crysis 3 and the Battlefield series, they make their games to run on PC and Console but have the reputation of knowing how to produce optimized games that take advantage of the hardware available to their customers. Star Citizen is another title that willl be released by a game designer who knows and relates to his client base. He has even come out and said that you will need a top of the line single card OR a dual GPU setup to run my game at these graphics settings.
So, no SLI doesnt work for every game. But Im sure as hell pleased with the 90% of games it does work on!
Anyway, I'm ranting. 2 GTX770 4GB cards in SLI will handle 90-100% of game titles for the next year or two. By then, a better card than the 970 or 980 will be out and the upgrade will be worth it.