To address the issue of retention/speed: the main point about using Alt.Binz with NZBs is that groups don't matter, as the files are indexed by Message ID; that is, all the crossposted group headers point to a single article on the server (or they should do if it's working properly). If one group deletes its header earlier than another, that won't make any difference to the article, since its Message ID remains valid. By the same token, there should be no reason for slower speeds, since Alt.Binz doesn't actually download from 'groups' at all (the option to 'Select Group' is for other reasons).
If an NSP was culling articles based on the largest group that holds a pointer to it, or deletes it when the first group header is deleted, I'd be very surprised and want to ask them why. It would mean that the related headers would have to be purged from all of the groups, regardless of 'retention', or the headers would point to nothing. So: if the article is available to *any* group in Alt.Binz, it doesn't matter what group is being listed in the queue.
