If your use case fits data.table then you probably want to use pytables in python. It's much faster than pandas when dealing with very large data sets, at the cost of some features you may or may not need.
The benefits from data.table are not as much processing very large data (anything above 10M observations is mostly outside of R's comfort zone on a reasonable machine, anyway), as much as the ease of performing operations such as indexed joins, aggregations, and so on.