Google groups makes feeds available for any given discussion group. Eight of them, in fact, by mixing and matching:

• 15/50 New [items]
• Where [items] are messages/topics
• Atom 1.0/RSS 2.0

For example: Feeds for the v8-users discussion group.

What is the difference between all these options? Most of these feeds seem to broadcast the exact same content, save for one option that has not updated since Aug 2009 (Oddly, it was the first one I selected, leading me to believe the feeds had been abandoned).

• I get the difference between "New messages" and "New topics" refers to receiving all the messages, or just the first messages of each thread.
• I understand Atom and RSS are simply different formats; is there any difference for the end-user experience reading the feed via Google Reader? I noticed the RSS feeds briefly flash some XML text before being properly rendered in Opera (Atom does not do this.)
• I can't see any difference between the 15/50 options...