If you already have a 770, then buying one more is a viable rather option than trying to sell off your old card and buying a higher end single card (which also is a viable option if you can sell it off easily for a good price. Plus you can later SLI your higher end card for even more performance.).
Most if not all games now a days will scale (almost) linearly with the second card. Also Micro stutter is no longer the issue is used to be. I am currently running 780Ti SLI and never have any micro stutter.