My database is pretty much on par with yours, and for the most part I have the exact same problem. It took about 9 tries before it successfully updated the first time (a hint....if it's going to work you will see a "time remaining" come up after a couple of minutes).

However, since then I've had extreme difficulty in trying to update. Some of the times when I get the 507 message it has updated some of my collection, but I'm not sure that everything is updated.

If you click on the blog link on the bottom of mygenres.com....in the comments for the top post...there are hints given for uploading larger collections, but I didn't really see much difference.