Is it worth it to try and find a way to use this graphics card with my iMac?

I have one of these sitting on my desk, collecting dust:

PNY Video Graphics Card VCGGTX7803XPB

I am using a 27" iMac with the following specs:

27-inch iMac with Retina 5K display
• 3.3GHz quad-core Intel Core i5, Turbo Boost up to 3.9GHz
• 16GB 1867MHz DDR3 SDRAM - two 8GB
• 2TB Fusion Drive
• AMD Radeon R9 M395 with 2GB video memory
• Magic Trackpad 2
• Magic Keyboard (English) & User’s Guide
• Accessory Kit
• Final Cut Pro X

I do all of my animation rendering so far with Blender.st, so local rendering isn’t a goal. Is there any way to utilize my old PNY card with the iMac, and will it make a worthwhile difference?

I have one of these as well, although I can’t say for sure it still works. I replaced it with a GTX 1050 and performance is pretty much the same for my wife playing WOW. I also did a speed test between my GTX 780 in her desktop and the GTX 970M in my laptop and the 970M was slightly faster.

Not sure if this helps you get some perspective or not.

You would need an external enclosure for the graphics card if you could even get it working with your imac as only AMD external GPUs are supported with recent hardware https://support.apple.com/en-us/HT208544