I have a gaming PC with very good hardware that I dont wanna get rid of. What activities can you do that pushes the hardware to its limits that are not Video Games?

I think the best thing is to learn how to make 3D models realistically and render them in video using blender, I think that would help push you to the limit but without gaming because your learning how to compare a photo of real photo and how to mimic to another, or you could try to learn animation like I do to help push the animation software to limit with your own stories by learning how to animate, write, direct, voice act, etc. The choice is up to you.

Ask yourself this what do you want to learn? 

Thanks for the advice. I’ve also heard that there are some very hardware intensive engineering software, do you know any? Thanks again.

You can learn to make music, to code, I am now learning to draw little by little and it seems comforting to me.

I mess around with Adobe Photoshop, Illustrator, and some of the Adobe video making software.  With a good processor and enough ram you can render videos pretty fast, or edit them in higher quality, which always helps.  Also I use some 3D sculpting and modeling software that would take a toll on a cheaper PC.  I personally enjoy Maya and Maya Mudbox.  I got them for free through school, but you might be able to do a free trial and check them out!

I also tried fruity loop studio, I think this can run on most computers, but it wasn't too much up my alley.  I prefer to just consume good music.