Thank you. I've learned a lot from this thread, and it certainly helped me render a wide night-scene lit only by 'super-ambient' street lights.

https://www.deviantart.com/nik-2213/art/Park-path-by-night-99pixel-Superfly-render-843031050

One gotcha: after much Googlin', I learned I did not need a RegEdit to turn on SCUDA for my twin GTX 750 Ti cards, their NVIDIA control panel let me toggle the option. As the 'program' list only found P7, I used the 'global' route. And, as each card had 640 cores, I was able to set 1200 bucket, leaving a few for Windows UI...