On my 700 it took about 2-3 minutes to index an sd card with about 1050 files - lrf and pdf books arranged in 6 folders containing about 175 books each.
However it took 6-7 minutes to index about 800 files of which about 650 were jpg pictures.
So I guess the number and type of files make a difference.
The one thing I would be leery about is dealing with non-lrf/pdf files (rtf, txt) that have lots of jumbled text - for example UC OCR's - since the Sony/700 software tries to make sense of them and that can take a while.
Better convert them to lrf first using Calibre and then load them on the 700