Sale 1:

Sold for Blizzardy Storm Reggaelator (16.5)

No outpost

Seller: https://backpack.tf/profiles/76561198084205929#!/compare/1494374400/1494547200

Buyer: https://backpack.tf/profiles/76561198079345240#!/compare/1494460800/1494547200

X = 17

Sale 2:

Sold for 13 keys

http://www.tf2outpost.com/trade/28904619 - B/O of 13

Seller: https://backpack.tf/profiles/76561198002757046#!/compare/1494115200/1494201600

Buyer: https://backpack.tf/profiles/76561198084205929#!/compare/1494115200/1494201600

X = 13

Sale 3:

Quicksold for 12 keys

http://www.tf2outpost.com/trade/29174851 - B/O of 14.5

Seller: https://backpack.tf/profiles/76561198079345240#!/compare/1494460800/1494547200

Buyer: https://backpack.tf/profiles/76561198209195433#!/compare/1494460800/1494547200

X = 12

Sale 4:

Sold with 1.33 ref for 12 keys

http://www.tf2outpost.com/trade/29176836 - B/O of 15

Seller: https://backpack.tf/profiles/76561198209195433#!/compare/1495411200/1496361600

Buyer: https://backpack.tf/profiles/76561198015753790#!/compare/1496275200/1496361600

X = 12

Sale 5:

Sold for Australium Tomislav (>11.5)

No outpost

Seller: https://backpack.tf/profiles/76561198015753790#!/compare/1497830400/1497916800

Buyer: https://backpack.tf/profiles/76561198069616176#!/compare/1497744000/1497916800

X = 12

Sellers:

16 keys:

http://i.imgur.com/QPNqpe8.png - 4 months

https://backpack.tf/u/76561198066195760

http://i.imgur.com/XmYUTi1.png - 3 days

https://backpack.tf/u/76561198016070169

http://www.tf2outpost.com/trade/29241246

Sales at:

12 (3x)

13

17

17 is a clear outlier, and the 4 month old seller at 16 proves that it cannot sell for that much. Excluding 17.

12 may have quicksold once, but the buyer of that sale re-sold for less than 12, and the other two sales at 12 took a while to sell.

Going with 12-13.