Upgrading current computer

Hi guys,

My current configuration is:

CPU: i5 4690K
Motherboard: MSI Z79 Guard PRO
RAM: Gskill 8GB
SSD: 970 Evo plus 500 GB
HDD: 4 TB WD Black
PSU: Corsair VS 550
Monitor: BenQ 2250-B, Highest resolution 1920X1080 (60Hz)

I am planning to play lastest games. But most of the time, I will be using the computer for editing (video, pictures) and for virtualization (VMware and Virtualbox). Also, for website development.

My current budget is around $ 600. So, please help me out on how to upgrade my current desktop.
Do I buy more powerful PSU? or
Do I buy a new graphic card? or
Do I buy a new monitor? or
Upgrade CPU, motherboard and RAM? If so, please suggest me a budget/new/more powerful CPU, motherboard and RAM combo.
Or any other suggestion would be appreciated.

Thanks in advance! I am waiting for your suggestion.
 
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