Money is not of the essence, i have a 980 of my own now and im wondering if i should sli the one i have or just sell it and get at TI. I only care about performance
Obvious answer would be to get two 980 Ti's and SLI them. But that wasn't the scenario that you posed. I will only say that Jay, from JayzTwoCents, recommended two 980's (not Ti's) in SLI for 4K resolution. He indicated that two 980's were higher performing than one 980 Ti. I've pasted the video and time index below.
if money is no object, go with the ti just for the increase in video memory - more capable of handing additional texture effects and mods as well as supporting Nvidia Surround with less strain at higher resolutions.
SLI gains you about 50% gpu performance of what that single card is capable of, but you're still stuck only being able to access the video memory from a single card which is lame.
I think it largely comes down to 4gb vram v 6gb and before anyone says it DX12 is too much of an unknown. You also have to take into account sli is not always supported and when it is you often have to wait a while after a game launches before good drivers are released
If money is no object you should start with the fastest single card like the Titan X. Then if you still require more power get a second one and SLI it. You can even go for tri and quad SLI.
Or wait and see what the DirectX 12 benchmarks look that should breath new life into all sorts of cards from the top down. Also your 980 is already DX 12 compliant at feature level 12.0
I would [and did] go with a pair of msi 980 ti gaming 6g cards. A single card will outperform a gtx 980 SLI in many occasions, or at least provide equal performance in others. Then in situations where SLI isn't used, like in basically every MMO, it'll work better than the single 980 [obviously].
Obvious answer would be to get two 980 Ti's and SLI them. But that wasn't the scenario that you posed. I will only say that Jay, from JayzTwoCents, recommended two 980's (not Ti's) in SLI for 4K resolution. He indicated that two 980's were higher performing than one 980 Ti. I've pasted the video and time index below.
I'm guessing he hadn't gotten the updates for the games, because they do a lot better than that now. My ti gets like 90-100 fps @ 1440p [140 or so for two tis].