To first clear your confusion around the terms:
GPGPU stands for General Purpose computing on GPUs
CUDA is the specific NVIDIA API to perform GPGPU only on their hardware
OpenGL is a graphics specific API and is vendor independent
OpenCL is a parallel programming compute API and is vendor independent
Compute Shaders are a way to perform general purpose computations within
a rendering system but without being part of a fixed rendering architecture.
They exist for OpenGL (https://www.khronos.org/opengl/wiki/Compute_Shader)
but also for other graphics APIs like DirectX (DirectCompute) etc.
OpenCL is not only built for GPUs and can also be used to write code
for example to run massive parallel computations on supercomputers.
NVIDIA develops their own ray tracer based on CUDA and GPU computing.
The project is called Optix (https://developer.nvidia.com/optix)
To your performance question. It depends, as always on your setup and use case.
Some people did already the effort to measure differences.
One paper for example is this:
Another one is this:
Or one thesis about it:
In their comparisons did CUDA often show good results. But when they for example used image processing algorithms that can be parallized very efficiently from the GPU then the comparison is nearly worthless compared what you might do in your path tracing code.
If you do not use any "classic" rendering, which you wanna combine your path traced results, I see not why you should use compute shaders for a pure path tracer. If platform independence is important OpenCL might be interesting for you since you then can take the code and run it on a complete other hardware for comparison. If you will stick to NVIDIA GPUs anyways you will likely get better performance using directly CUDA.