We run tens of thousands of streams in parallel.. So that's not a problem. :)
I'm just realizing that GPUs could be a viable alternative to specialized (eg, expensive) encryption offload engines or very high end (eg, expensive) v4 Xeons with many, many cores. However, it is rather hard to find data on the bandwidth at which GPUs can process a given cipher. I'm just now starting to look into this, so I could very well be mis-understanding something,