Is this system worth upgrading?

Jan 31, 2019
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Hi,
I have an old system that my son's been using to play CSGO, Rainbow 6 Siege, and Destiny 2. He mentioned that it seems to be struggling with the last one, so I was considering doing something about this for his birthday. Specifically, I was thinking about adding RAM and upgrading the video card. However, it's fairly dated so I'm not sure if it would be appropriate for the system. Here are the current components:

Mobo: Gigabyte P55A-UD4P (LGA1156)
CPU: i7-860 Lynnfield 2.8 GHz
GPU: Radeon HD 5870 (Cypress XT)
RAM: 4 GB DDR3 1333
PS: Antec TruePower New TP-650 ATX 12V V2.3

So, my question is if upgrading the video card is a reasonable route to take. The options I was considering were: GTX 970 (in my current machine) or buying a GTX 1060/1070/1070 ti? Are any of these good matches or are they overkill?

Thanks for your feedback.

-J