If you take the same basic GPU card, but one version has 50% higher number of CUDA cores than another, will that higher number make any perceptible difference in FSX or P3D performance? If so, what will the difference be?

IMHO no impact whatsoever:

From the nvidia site: https://developer.nvidia.com/category/zone/cuda-zone

 

 

CUDA™ is a parallel computing platform and programming model invented by NVIDIA. It enables dramatic increases in computing performance by harnessing the power of the graphics processing unit (GPU).

 

 

and

Not anymore. With CUDA, you can send C, C++ and Fortran code straight to GPU, no assembly language required

AFAIK there  is very lttle if any parallel code in FSX and CUDA was not around in any great strength, when FSX was being programmed, so the chances of any positive impact would be minimal.  Not sure if any FSX add-ons use parallel computing techniques.

 

Some of the features that will have an effect is to match the VRAM to Monitor size(s), GDDR5 VRAM, Bandwith, drivers, visual settings in and ex-game plus the balance between the cpu/mobo/RAM and gpu  and the OS Including the FSX Virtual Address Space and the program code.

 

Make no mistake a powerful video card can make a difference even in FSX where the cpu does most of the computing but then all that data has to rendered in a fast smooth display and the gpu handles that,

Regards

pH