Sale 1:

Sold for Aces High Fed-Fighting Fedora (Mini at 20.5 below) + 2 keys

http://www.tf2outpost.com/trade/28500422 - No B/O

Seller: http://backpack.tf/profiles/76561198147356475#!/compare/1474502400/1474588800

Buyer: http://backpack.tf/profiles/76561198045139940#!/compare/1474502400/1474588800

X = 23

Sale 2:

Sold for Orbiting Planets Lucky Shot (21) + ~0.5 keys in stranges

http://www.tf2outpost.com/trade/28494335 - B/O of 23.5

Seller: http://backpack.tf/profiles/76561198017901187#!/compare/1474070400/1474156800

Buyer: http://backpack.tf/profiles/76561198110459728#!/compare/1474070400/1474156800

X = 22

Sale 3:

Sold for 17 keys + 14.55 ref (0.6)

No outpost

Seller: http://backpack.tf/profiles/76561198045139940#!/compare/1476835200/1476921600

Buyer: http://backpack.tf/profiles/76561198003539819#!/compare/1476921600/1477094400

X = 18

Aces Fed Mini:

http://backpack.tf/suggestion/5819cea18667477b5e4eb5d5

Sellers:

25 keys:

http://i.imgur.com/ZdlLWc4.png - 3 months

http://backpack.tf/u/76561198086948995

Sales at:

23

22

18

18 looks like a bit of an outlier. Excluding 18

Going with 22-23