My dataset is still small, but you can scale a single TC db to nearly arbitrary size (8EB). It can also write millions of kv pairs / second.

Vertex.js can't quite keep up with TC as its written in javascript. However, it does let you batch writes into logical transactions, which you can use to get fairly high throughput.

The source isn't open as its fairly specific to my app, http://luciebot.com/. I'd be happy to chat about the details without releasing the source. richcollins@gmail.com / richcollins on freenode.