You should really implement support for the If-Modified-Since header and if-none-match header. Every* RSS client is going to send that header on refreshes and

You should really implement support for the If-Modified-Since header and if-none-match header. Every* RSS client is going to send that header on refreshes and if you haven't posted something new since the date-time in the header, you can simply return a 304 not modified response (which is tiny). You can get the best of all worlds with a short TTL on the CDN edge you will have low bandwidth utilization and fast updates.