If i edit an id3v2 tag, I get around 350k/sec regular, and 700k w/ the --whole-file switch

The problem with id3v2 tags is that they are at the beginning of the file, rather than at the end, like id3v1 tags. If you insert a id3v2 tag, or when its size increases, the mp3 frames are shifted to a different location in the file. As far as I can tell, rsync cannot detect this and compares the whole file, only to find out it has to transmit everything again, because none of the file parts are identical.

Pim