1. bitrate refers to how much music is packed into 1 second, so higher bitrate usually means better quality. However, that means the file is bigger, which takes longer to download.

2. Proxy mean connecting to another computer which handles all your requests. This adds another link in the chain between you and the files, which may slow down your connections.

3. IP addresses don't contain personal info, but somewhere (like your Internet Service Provider), your IP address may be linked to your info.

4. Many ways. . . but too complex to describe quickly here. Search google or wikipedia for "packet preferencing" "p2p throttling" or "port blocking"

5. The available upload bandwidth of the other computer, and your available download bandwidth, and (less so) your computer's ability to process the information.

Re the audiobook, it sounds like you have a slow or very busy host. The easieast possible solution is to do more searches using more specific search terms. As new sources are found (if possible), their combined upload speeds should get the download coming faster