I think we are missing the point of making a balanced and complete system here.
the real question is what type of screen are we running. if it is a 1080p @60 hz then all performance over 60 fps is for nothing.
so if we use the r9 280x as a reference (it is the same card as the 7970), and we should use this card since it has closer to recent drivers and such and using an article from 2 years ago will not be good for knowing where we really sit.
so lets see
watchdogs 45-50 fps average
http://www.hardocp.com/article/2014/08/18/watch_dogs_performance_image_quality_review/6
shadow of mordor 60fps
https://steamcommunity.com/app/241930/discussions/0/613937942896250303/ not that great of a review but i read at kitguru they got 76fps with a gtx780 so it sound about right
here is another review of a bunch of games unfortunately they run almost all of them 1600p which is twice the pixels of 1080p. If they get 45 fps at that resolution it is safe to assume you will get 60 fps at 1080p
http://www.hardocp.com/article/2013/10/07/asus_r9_280x_directcu_ii_top_video_card_review/4
In the end you have to ask yourself if it worth the extra money to gain may 15 fps at best in most games.
I can tell you that the farcry4 and assasins creed unity run at about 35 fps all max settings at 2560x1440 with a gtx970 running at 1505/8000. this is a nice overclock that puts it even with a gtx 980 in benchmarks.
In the end I would not upgrade if I were using a 1080p monitor. I would wait for the new AMD cards to come out and let there start another price war and see where things settle out at.
on the other hand if you want to guarantee 60fps in every game then the $400 investment may be worth it to you.
if you are running a 120Hz monitor or a 1440p monitor then yes get a gtx970 all the way.
http://www.hardocp.com/article/2013/10/07/asus_r9_280x_directcu_ii_top_video_card_review/4