[Vladimir Burneski]

Some applications are made to work better with openCL and some with CUDA.
CUDA is technology developed and used only by Nvidia, though they also use the openCL technology but they focus on their own, CUDA. That said, AMD’s GPUs are better when it comes to openCL performance.

As for the program Vegas Pro, it supports both CUDA and openCL, but works better with openCL than with CUDA. The best CUDA based cards that work with SVP are the Nvidia GTX 500 series. This is because MainConcept and Sony AVC havent updated their support ( well at least for rendering ) since 2011, which is why those 2011 cards are the best ones when it comes to CUDA rendering.
I havent done tests on my own because I dont own an AMD card, but as far as my research goes, you can get much better performance ( both previews and rendering ) from openCL than with CUDA.

In short, openCL works better with Vegas Pro because it has better support than CUDA has in this software. So if you wanna buy a GPU to get a better performance in Vegas Pro, I’d recommend you to buy openCL based card.

Have a look at this.
https://images.anandtech.com/graphs/graph7481/59491.png