I play most all games on ultra settings with a 4GB 680, and the 980 is literally 2x the performance. A 970 is only slightly slower than that so I'd be safe to say that you will have no issues running these games with your new 1080p monitor.
The i5 is also about 3x more performance in games than your current CPU, so no you won't have any issues. IF you wanted to go 980, the motherboard and CPU choice is perfectly fine. If you ever want to do SLI later for whatever reason the 4670k won't hold it back and you'll need a Z87 or Z97 board to do so. Just check with me to make sure everything is dice.
Also, AC Unity is locked at 30fps. The 970 will have no issues there.
Also, don't ever be afraid to upgrade as that's all part of the game. It's one of the reasons why PC gaming is so much better than console gaming. Need more performance for that extra bit of AA? Pop a new graphics card in if the wallet permits.