Thanks a lot for such a detailed answer.
Yes, I forgot to mention that they are one dimensional resources which is why I'm using y=1, z=1 for the numthreads definition.
I already figured that I might need to do something like that (dividing into thread groups), but I didn't really understand the concept in association to the hardware. Your explanation helps me a lot there
Indeed 1-2 Million is not that much when it comes to GPU computing ... just in relation to 216 (65535) it is quite a step which I didn't know how to take.
Thanks for the great help (+rep)