I’m betting the “medium quality” is your problem. Since DV is a set stream of 5:1 compression, you probably cut the image quality in half by using medium, but I’ll bet the file size is the same. DV is DV.
I assume you also cropped out 2 pixels at the top and 4 at the bottom as well. You need to do that to get DV 720×480 if you were working in 720×486 on the Media 100.
You really might just make things easier by going to tape from the media 100. Especially if you have fw out of the media 100. That would be the conversion. There would be no more conversion going into FCP via firewire.