Make RSS screensaver show more articles?
Sure — the easiest way to do this is to edit the screensaver's Quartz composition file. It's located at

/System/Library/Screen Savers/RSS Visualizer.qtz


In order to edit this, you'll need Quartz Composer, which you may already have (if you installed an old version of the developer tools), or you can download it with the Graphics Tools package here.

Open the aforementioned file, click on the "RSS" macro patch, and change the News Count to your liking:



Then save the file or make a copy and put it in ~/Library/Screen Savers.



Edit: I just spent a while trying to figure out if you can expose this option via the options panel, but it seems there's some very specific interface in place for the RSS Visualizer screensaver (see /System/Library/Frameworks/ScreenSaver.framework/Versions/A/Resources/.Quartz Composer.saver/Contents/Resources), so you can't do it if you also want to see the normal RSS options.