Time to move table to new tablespace

I'm considering the migration of an existing large (2.3TB) table to a new
tablespace. The table size, according to the '\dt+' command:

public | city_summary | table | altosresearch | 2345 GB |

Are there any considerations - besides the usual disk and network IO
constraints - that I need to take into account when estimating the amount
of time that would be required for the following commands to complete?

psql> create tablespace 'newstorage' location '/some/new/path';
psql> alter table city_summary set tablespace = 'newstorage';

Any other recommendations are welcome, such as "You are an idiot for not
using partitioning in the first place" :)

--
Jason L. Buberel
CTO, Altos Research
http://www.altosresearch.com/
650.603.0907