What's the difference between the plethora of RSS feeds Google groups offers?

Question

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...

Answer 1

As you've noted, there are three categories that divide these up resulting in 8 different feeds:

15 vs 50 - This just tells you how many items appear in the RSS feed. Depending on how busy the group is and how often your RSS reader checks it, collecting only 15 messages could mean missing out on some if 20 had been posted. On the other hand, if the group gets very large postings a 50 item feed could overwhelm a basic RSS reader.

Messages vs Topics - Like you say, the difference between getting all messages or the first one of each thread.

RSS vs Atom - As a user there isn't really any difference between one or the other. Most of the differences only matter to someone programming the feed creation or reading process.