After a long running discussion, Slic3r will calculate flow using the same formula Nophead has published on his blog a few years ago (which it did already in some cases). But the difference is minimal, and Slic3r 1.2.0 will have other interesting features too, for example to get correct dimensions of parts. This will be interesting to try out!
http://forums.reprap.org/read.php?263,273929,388183#msg-388183