DOC: Timings/space of datatypes in the docs
Would it be useful to have a section in the docs discussing:
- how much space pandas objects take up (vaguely how many rows \* columns equates to size space, if I have an xGb csv how big will it be in pandas/HDF5/etc.).
- how quick are some standard operations are likely to be (e.g. read_csv in/merge/join/etc. vs data size).
- how do these compare to other platforms (?)

Probably distinct from comparing _functionality_ (although that may also be interesting) e.g. like numpy do it for _features_ against matlab here: http://wiki.scipy.org/NumPy_for_Matlab_Users) e.g. #3980
