Safari :: Efficiently Delete Excess Favicons?

Deleting all Safari's favicons often seems to speed up Safari 5.0.6 (in OS X 10.5.8 on a late-2008 Intel MacBook Pro), but it slows me down when I use long Bookmarks lists with generic-looking entries.  I've read that Safari saves a favicon for every site it visits (if it finds one)!  My webpageIcons.db file is 9.8 MB now (versus 156 KB for Bookmarks.plist and 788 KB for HistoryIndex.sk).  Is there an efficient way to save just the favicons my Bookmarks lists use, and delete all the others?  Wouldn't this speed up Safari almost as much as deleting them all?

Info:
MacBook Pro (15-inch Late 2008), Mac OS X (10.5.8), Safari 5.0.6