I came here with the same question....
I've no idea but Im currently using the built-in plugin and it's still only on 16% after 2 days. I am worried about my external harddrive being undr pressure for so long ! (where I'm putting the masters). At this rate it will take 2 weeks! So far there is no semblance of my aperture folder structure, but from what I understand that happens after the photos have been imported.
sorry not to help more!
I tried the plug-in (got a trial version of LR5) and after making sure that my entire Aperture Library was referenced, started it - and made sure to tell it to leave the files where they were! To my dismay (1) a lot of photos that I would have expected to be imported came back with errors - even though the ORF Olympus RAW file was a supported camera and more importantly (2) a lot of my photos that were in particular folders, now found themselves in folders based upon the date the photo was either taken or imported into Aperture. Now I read about this - but it is only supposed to happen if you had a managed library and then LR would move the image files into folders based upon dates.
My library had about 68,000 images and after about 6 hours it was up to 30% or so, so I just clicked on DONE to see how it was handling my folder structure.
I am now trying with an application called Aperture Exporter (they have a trial version, but it has limitations on how many photos it will import) and it seems to be handling the export much better. It is keeping my folder structure intact, keeping my metadata (mainly keywords) and any photo that had adjustments in Aperture applied it gives you the option of exporting the original RAW/JPEG file along with a copy of the adjusted one - either as a JPEG or TIFF. Only "issue" would be that you have to have enough hard drive space to duplicate - at least initially - your entire photo library. Don't see an issue to do the export one folder or project at a time (at least not in the demo version).