We plot the cumulative impact factor that the most-cited Letters in PRL would have in 2006, if published separately. The 500 most-cited Letters published each year would have an impact factor of around 20; the 250 most-cited Letters would have an impact factor of over 25; and so on. The actual 2006 impact factors of PRL and of Reviews of Modern Physics are also shown. The data are from the Web of Science (WoS; collected September 2007) and Journal Citation Reports (JCR), Thomson Reuters, for 2006.Reuse & Permissions