i'd go with the strongest card you wish to buy. obviously you don't upgrade very often so get the best card you can now. then when you upgrade to a new cpu/mobo you're already running a nice strong gpu that will last.
i don't buy into trying to figure out which card will somehow be "balanced". there's so many variables to that and it changes from game to game. so i just suggest grabbing the best you can/want once the newer cards are actually available to buy. unless you're getting the absolute top of the line, then you'll get most of the performance out of it. people love to throw that word "bottleneck" around like it is somehow a crippled card. it just means the cpu won't feed it enough work to do so it won't run at 100%. that's only at 1080p mostly. if you use a higher resolution, then the "bottleneck" is not really there as the card has a lot more work to do pushing the higher resolution.
i just upgraded my 4690k system to a 3700x so i understand about not upgrading regularly and this is how i tend to go about buying parts.