OCing your CPU will be no problem with this setup but the 970 will struggle from time to time with quite a few games @1440p if you want them to run at high/ultra settings. You would need a second 970 or a 980ti to do this without any problems, especially in newer or demanding games like GTA V, Shadow of Morder and so on.
But it will do okay at 1440p with most games if your lower the settings a bit. But in generell it will be totally fine and will also run any games from 2014/13 or older at max settings i guess.
Only thing id change is the PSU, not because of it's quality, but because of the 620w which is quite alot for this system but not enough for adding a second 970 after price drops in the future for example.
If you want to stick...