When working with P2 in Avid, there is no need at all to convert to Quicktime. It would have been faster and better if you had brought the files into Avid, and kept them at their native resolution. I have no idea what flavor of QT you have converted to (hit CTRL-I in the QT player and it will tell you what codec is used) but from the 6 Mbps figure you mention, it does sound like a severe quality hit, coming from DV, which is 25 Mbps. Also, if you convert P2 media using FCP, you are very likely changing the gamma of the files, even more so if you chose H264, so by now, you are likely pretty far from the original. Sorry.
Drive space is cheap these days. Never throw away your originals. For file based media, have at least two copies at your disposal at all times.