Your current rig in pretty out dated and the psu has aged well but you are around the point in a psu life span where it may soon go out and that is un safe to new pc parts. You say you want to play at 4k or close to it well honestly the 970 is a great card but it won't do 4k for you, it is the king of 1080p, but when you play at 4k you want to do it right, the amd 300 series is coming soon and that may be a good option to wait for. Honestly you want to build a pc at a perfect time with a lot of new tech coming out soon. I would attempt to sell my current rig on craigslist if I was you for like 300$ if you can get that. If you can hold off on a new rig until the new intel i5 and the amd 300 series drops, save up until then it will be worth it in the long run. That monitor you selected is amazing but if your rig doesn't have the power to use it then it's pointless.