Sale 1:

Sold for 10 keys (and a steel six pack)

http://www.tf2outpost.com/trade/27768083 - B/O of 11

Seller: http://backpack.tf/profiles/76561198043806938/#!/compare/1453968000/1454054400

Buyer: http://backpack.tf/profiles/76561198164135796/#!/compare/1453968000/1454054400

X = 10

Sale 2:

Sold for 9 keys and a little more than half a key in taunts

http://www.tf2outpost.com/trade/27777866 - B/O of 10.5

Seller: http://backpack.tf/profiles/76561198164135796/#!/compare/1455868800/1455955200

Buyer: http://backpack.tf/profiles/76561198168259682/#!/compare/1455868800/1455955200

X = 9 + 0.5

X = 10

Sale 3:

Sold for 11 keys

http://www.tf2outpost.com/trade/27996408 - B/O of 11

Seller: http://backpack.tf/profiles/76561198072621989/#!/compare/1458950400/1459036800

Buyer: http://backpack.tf/profiles/76561198198583623/#!/compare/1458950400/1459036800

X = 11

Sale 4:

Sold for 9 keys + Kazotsky Kick

http://www.tf2outpost.com/trade/27694848 - Deleted B/O

Seller: http://backpack.tf/profiles/76561198130205261/#!/compare/1452931200/1453363200

Buyer: http://backpack.tf/profiles/76561198208062409/#!/compare/1452931200/1453276800

X = 9 + 1.5

X = 11

Sale 5:

Sold for 9 keys + ~1 key in items

http://www.tf2outpost.com/trade/27811961 - B/O of 11

Seller: http://backpack.tf/profiles/76561198073203297/#!/compare/1454745600/1454832000

Buyer: http://backpack.tf/profiles/76561198073203297/#!/compare/1454745600/1454832000

X = 9 + 1

X = 10

Sale 6:

Sold for 11 keys

No outpost link available

Seller: http://backpack.tf/profiles/76561198002757046/#!/compare/1459382400/1459468800

Buyer: http://backpack.tf/profiles/76561197983585579/#!/compare/1459382400/1459468800

X = 11

Sale 7:

Sold for Smoking Fr-0

No outpost link available

Seller: http://backpack.tf/profiles/76561198168259682/#!/compare/1455955200/1456041600

Buyer: http://backpack.tf/profiles/76561198150783829/#!/compare/1455955200/1456041600

Sale 8:

Sold for Dead Presidents Sultan’s Ceremonial

No outpost link available

Seller: http://backpack.tf/profiles/76561198002757046/#!/compare/1457769600/1457856000

Buyer: http://backpack.tf/profiles/76561198072621989/#!/compare/1457769600/1457856000

Sellers:

11 keys:

http://puu.sh/o6OF0/d134f28ea5.png - 8 days

12.5 keys:

http://www.tf2outpost.com/trade/28028522 - 3 days

http://www.tf2outpost.com/trade/27781861 - 2 months

http://www.tf2outpost.com/trade/28005111 - 1 week

With the abundance of pure sales here, it would be best to use this hat to update the other two outdated hats

Buyers:

10 keys:

http://www.tf2outpost.com/trade/27934308

The Sales:

10 (Full pure)

10 (Mostly pure)

10 (Mostly pure)

11 (Full pure)

11 (Full pure)

11 (Mostly pure)

Given how quick some of the 10 key sales happened, the buyer at 10 keys, and lack of sellers at 10 keys, it would be best to exclude 10 from the range.

Going with 11 flat