Help me rebuild my PC

Hey everyone

Let me first explain my situation. My current pc is a 4 yr old Alienware aurora r4. Yes yes I know, how dare I waste my money on a pre built Alienware. At the time I didn't have much money and they allowed me to finance a new pc over a year with zero interest so it was my only option.

Thankfully I'm now in a position to start upgrading/transitioning to my own custom build.

I have upgraded the video card recently, moving from Sli 660s to a gtx 970.

So the current components in my pc are as follows:

Intel core i7 3820 @3.6 ghz (10mb cache) Nvidia Gtx 970 Motherboard unknown 16gb of DDR3 ram 1600mhz Power supply unknown 1tb hard drive

I would like to build a new pc using at least my existing graphics card. Hopefully with the capability to run 4k on medium settings and 1080p on ultra.

Are there any budget upgrades I can make to see some significant performance increases. Specifically in CPU heavy games like mmos.

Thanks in advance for any advice given.