LOL I re-read the article and found the specs. I really read it but somehow managed to skip the paragraph or something :-?

Anyway, my point stands. I'd use a single instance in which the dataset fits in memory, just for completeness. Then, you can compare one mongo with the full dataset to one stampede.

As you said, the aggregated data will still make Mongo suffer, but it will be a better comparison. I still like the 3-shard setup, though. It's also a good reference point.