Considering the price, the invesment is not really worth it (it's pretty much the same thing with every hight-end card, at some point, you only gain 10% perf per 100 more $). They did a great job with this two first generations of Maxwell in energy management but we won't probably see a real graphic gap until the 20nm GPU release.
In fact, if you are looking for a new card the GTX970 is 200$ cheaper for an average 10fps difference according to the various benchmarks I've seen
(Crysis 3, 2560*1440, Hight, SMAA, DX11 = 56fps for the 970). Well, of course these have been made on review cards send to these journalist by the manufacturer and it's well known that these models are generaly overclocked for best perfs
(around 10% or 20%).