I'm re coverting just under 400 DVDs for a new player and am having a very similear problem with 8.1. When copying the disc to a hard drive the speed drops to .2 MB/s. 8.0.8 works just fine. Most of the discs are not new at all. We normally don't buy anything till it gets to the $5 to $10 range and at that point they have usually been out for several months.
Sometimes 8.1 works perfect, other times, once in a while, there are problems. I still have a problem when running a large batch getting stuck, but I just copy the entry, cancel and restart. I don;t think I've seen a version where this didn;t happen. It's annoying, but DVDFab is still the best out there, IMHO.