Chieftec should be reliable enough, even if not perfect, but that can wait for another day.
As he is willing to wait, and is talking about 4K in a year or so, it would be a better idea for him to wait, as newer cards in his time frame are likely to be substantially faster in the 4k space and just get a temporary, cheap, faster card to make his 1080p 144Hz experience more pleasant if he really has the itch now. Neither the 970 or 980 are that great at 4k really.
He has a 6870, so he can get a substantially faster card for under £100, and the £150-200 saved can go to much better use once newer cards are out/the current gen have reduced with age.
Bear in mind what he is coming from!
@OP
The 7950 Boost (the 7950 is slightly slower, the 7970 and 7970 GHz edition are faster) is not far off your old 770
http://www.anandtech.com/bench/product/1033?vs=1037
If you are happy with that level of performance to hold you by, given the price of the 79**, this would be the economic way, and then come 4k, you can re-evaluate all the cards and spend the money saved on the best 4k card you can get at the time, which may well be better than the 970s.
Is getting the best you can NOW more important to you; or simply getting something decent that will improve your 1080p experience, and then getting something suitable later and trying to make use of your money effectively?
With your CPU you shouldn't really notice a major bottleneck on any of the options in most cases, just bear in mind your PSU may struggle with some dual card setups.