I remember reading a blog post of the peculiarities of GPU programming and the post noting that for most modern graphics cards (at the time) if you can keep your computable data in chunks no bigger than 64kb a piece you can expect to see enormous performance gains even on top of what you'll see by using openCL/CUDA because of a physical memory limit on the actual GPU itself.

I also remember thinking that a 64kb row size for DynamoDB was very odd.

I wonder if these things are at all related.