Hello,
Been a while since I looked at this stuff. But essentially you want the best GPU for performing parallel programs and Nvidia and AMD are very different there, you'll need to do some reading.
AMD V Nvidia
https://www.electronicshub.org/cuda-...am-processors/
If you know the software/libraries, you should be able to work out if you need cores over clock speed etc or whatev they grade them by now. The fact that he has listed Nvidia libraries would push me towards Nvidia. I love AMD but user support is better for nvidia as well.
If you choose to go with the CUDA, then "Best Budget GPU for CUDA acceleration..." type write ups etc.
Steve
Ps. There are really only highend cards, the rest have chipsets and functions removed, smaller specs etc to fit a performance/price range.
List for Nvidia by CUDA cores might be a better link:
https://gist.github.com/cavinsmith/e...9eaa8775e3284e
Pps. If you know any gamers talk to them, they will always have a 2nd hand card or be planning to upgrade soon. Not that I'd suggest gumtree for video cards, but, a cheap second hand $300 GTX 780ti is 2880 CUDA processors versus your GT 640 at 384 CUDA processors. That's 7.5 times the processors, a bucket load more memory and newer faster tech included.