I can only say: 'congratulations'. My best results are a few 4,2 l/100km. I found this very good... Compared to other bikes (VFR800, VFR1200, FZ1) it actually is. They are in the 6 to 7 and + zone. But compared to you I need to be humble.
Compare yourself to others with CBF600s
I do the same and depending on the other F650 riders' style they're in the 3-point-something and the 4-point-something range. I've seen someone over 5l/100km, but he's experimenting with a Power Commander, so it's not a stock bike
In the beginning it seemed that it's easy to be in the low 3s range, and straight 3l/100km is not that easy, but doable. It took a few weeks/months to reach it in a slow, conservative style.
Since then I got much better (and crazier) thanks to these hypermiling sites where I could learn about other techniques than just being gentle with the throttle, using the highest gear and try to avoiding braking by timing and leaving distance where approppriate. These are mostly valid and useful tips but I learned that there's much more and I can even have fun with them
And I learned that other riders (at f650.hu, for example) can think so simple... they still believe I reach these averages simply by going slow.
Of course I go slow but the belief that it's so simple hurts my pride (Even if it would mean that I had so much self control that I can only dream about )