ccoo84 :
After SLIing my gtx 770, I will never again go it alone with just 1 card. SLI is Off the Charts rad,.I bought my 2nd gtx 770 in August or September the same month before Nvidia announced the GTX 970's and 980's I was fridge pissed!! I am currently playing Shadows of Mordor and I can't Play it smoothly on ultra HD texture expansion, and I have GTX 770 Sli- I wish I would have bought the 970 and upgraded to 970 SLI when I have money, but since I bought that 2nd card I'll have to wait to buy the GTX 970. If your are anything like me you want to the best graphics and if it were last year it would be ok to buy the GTX 770 but not no more! good luck, I hope this is food for thought!
Sorry to bump an old thread but I am in the exact same position. Bought a single MSI GTX 770 Lightning edition in 2013 and SLI'd during the price drop when GTX 970's and 980's were announced. Yeah the performance is great and all (can max out Farcry 3) but with the majority of 770 cards being 2GB, you will find the VRAM becoming a bottleneck very quickly. You can see in the below screenshots that Shadow Of Mordor is taking up all 4GB of VRAM across both cards. Facry 3 isn't bad, but I can imagine Farcry 4 will be the same as Shadow Of Mordor.
http://imgur.com/a/FhTei
http://imgur.com/a/KSguf
To the OP, I would recommend going for SLI GTX 970 or a single GTX 980. Going for a single GTX 970 actually performs lower than SLI GTX 770. You can compare the Firestrike benchmarks below:
Mine (SLI GTX770 and AMD FX-8320) -
http://www.3dmark.com/fs/3061366
Single GTX 970 and AMD FX-8320 -
http://www.3dmark.com/fs/2841313
SLI GTX 970 and AMD FX-8320 -
http://www.3dmark.com/fs/3662352
Single GTX 980 and AMD FX-8320 -
http://www.3dmark.com/fs/3610654
Out of the four options the one with the most performance for price is a single GTX 980 as it offers performance closest to SLI GTX 770. The option with the most performance regardless of cost is SLI GTX 970. The option with the least performance is a single GTX 970. SLI GTX 770 is in the middle, although you will hit a VRAM bottleneck quite easily, especially for future games.