http://www.tf2outpost.com/trade/13027129 - B/O 6 buds

Sold for Miami Nights Halogen Headlamp(~1.9) + 3 buds + Big Kill = ~5.4 buds

http://www.tf2outpost.com/trade/13442665 - B/O 6 buds

Sold for TF2 Logo Anger(~2.5)

http://www.tf2outpost.com/trade/12560848 - B/O 4 buds

Sold for Terror Watt Capo's Capper(no price, and not enough data to make one)

http://www.tf2outpost.com/trade/12195530 - B/O 7 buds

Sold for duped Roboactive Trilby(~4.8) - the current price is based on the duped one

http://www.tf2outpost.com/trade/11691437 (older trade)

This one looks to have sold for a Stormy Storm KE(~5.1)

http://www.tf2outpost.com/search/141770657 - B/O of 5 buds currently on outpost

Going by the quantitative offers and calling the Anger sale an outlier, and factoring in that current B/O of 5 since there was a couple sales above it, we get a range of 4.8 - 5