Sales supporting the price:

Sale 1:

Sold for Cloud 9 Tungsten Toque + ~3 keys in taunts

http://www.tf2outpost.com/trade/27909230 - B/O of 14

Seller: http://backpack.tf/profiles/76561198238854082/#!/compare/1456905600/1456992000

Buyer: http://backpack.tf/profiles/76561198141607391/#!/compare/1456819200/1456992000

X = 13 + 3

X = 16

Capped by B/O of 14

Sale 2:

Sold for:

Smoking Carouser's Capotain

Mannrobics (2)

Festive Rocket Launcher (0.8)

Pink Bill's (2.5)

http://www.tf2outpost.com/trade/27894558 - B/O of 12

Seller: http://backpack.tf/profiles/76561198018528305/#!/compare/1456300800/1456473600

Buyer: http://backpack.tf/profiles/76561198167018159/#!/compare/1456387200/1456560000

Mini on the Capotain isn't absolutely necessary here, the items together are 5 keys, the unusual would have to be less than 7 keys to make a difference here, which is impossible, due to buyers at higher than 7.

X = 12

Sale 3:

Sold for Spec. KS Strange Festive Huntsman with ~7.5 keys in parts?

Seller's backpack is unavailable

Buyer: http://backpack.tf/profiles/76561198018528305/#!/compare/1454140800/1454227200

X = 10 keys

Sale 4:

Sold with Stormy Dapper's Topper for Searing Dapper's Topper

http://www.tf2outpost.com/trade/27879697 - B/O of 14 keys

Seller: http://backpack.tf/profiles/76561198070506279/#!/compare/1456128000/1456992000

Buyer: http://backpack.tf/profiles/76561198090956917/#!/compare/1456300800/1456387200

X + 17.5 = 23

X = 5.5

Rounding to 6

Sale 5:

Sold with ~8 keys in items for Orbiting Fire Professional's Panama

No outpost link available

Seller: http://backpack.tf/profiles/76561198167018159/#!/compare/1456646400/1456819200

Buyer: http://backpack.tf/profiles/76561198067008321/#!/compare/1456646400/1456732800

X + 8 = 16.5

X = 8.5

Rounding to 9

Additional sales:

Sale 6:

Not sure, possibly traded to alt

Seller: http://backpack.tf/profiles/76561198090956917/#!/compare/1456732800/1456819200

Buyer: http://backpack.tf/profiles/76561198069842576/#!/compare/1454227200/1456819200

Sale 7:

No clue. Item histories don't match anywhere.

http://www.tf2outpost.com/trade/27512132 - Deleted B/O

Seller: http://backpack.tf/profiles/76561198031007256/#!/compare/1451462400/1451635200

Buyer: http://backpack.tf/profiles/76561198191189210/#!/compare/1451289600/1451635200

Sale 8:

Same as the previous sale. Weak compare links.

Seller: http://backpack.tf/profiles/76561198122802981/#!/compare/1451635200/1452326400

Buyer: http://backpack.tf/profiles/76561198142994480/#!/compare/1451980800/1452758400

Sale 9:

Couldn't trace this sale

http://www.tf2outpost.com/trade/27907606

Seller: http://backpack.tf/profiles/76561198067008321/#!/compare/1456646400/1456732800

Buyer: http://backpack.tf/profiles/76561198238854082/#!/compare/1456646400/1456732800

The strange part and the Strange Crossing Guard both went to the buyer, but that was all I could trace.

Buyers at 10 keys:

http://www.tf2outpost.com/trade/27914809

http://www.tf2outpost.com/trade/27760327

http://www.tf2outpost.com/trade/27013589

Sales at:

14

12

10 (countered by buyers)

9

6

Going with 12-14