Your build is solid, there really isn't much you can improve on. You could upgrade your GPU but from now until the next generation which isn't far away, your 970 is fine for the job and wont see the value upgrading to something now.
I'm not sure what Counteragent666 is on about, to get 16GB you'll need multiple Dimms anyway. If i think what he meant was differing memory sticks then yes i'd keep them the same but its not a problem here. Usually the advice is given if populate all dimm slots it can stress the memory controller more but thats only a concern if you overclock past intended clock rates you might consider restricting the amount of memory sticks.
16GB system memory is the sweat spot but if you're itching to spend money, maybe...