Another scenario is that user A is sharing files F1 and F2; user B is sharing file F2. You want to get F1 ASAP, but your client keeps downloading F2 from users A and B. In this case, it would be optimal to download F1 from user A, but keep downloading F2 from user B (because he does not have F1 anyway).
Is there a way to force eMule to queue for a specific file without stopping all the the other downloads? Changing priority does not seem to help much