Sale 1:

Sold for 16 keys + 5 keys in items

http://www.tf2outpost.com/trade/28242975 - No visible B/O

Seller: http://backpack.tf/profiles/76561197999873164#!/compare/1466294400/1466380800

Buyer: http://backpack.tf/profiles/76561198035547951#!/compare/1466294400/1466380800

X = 21

Sale 2:

Sold for Circling Heart Katyusha + ~2 keys in items/pure

http://www.tf2outpost.com/trade/28276012 - B/O of 20, Seller confirms sale (Legend)

Seller: http://backpack.tf/profiles/76561198035547951#!/compare/1466467200/1466553600

Buyer: http://backpack.tf/profiles/76561198056465586#!/compare/1466467200/1466553600

X = 20 (Capped by B/O)

Sale 3:

Sold for 18 keys + Pro. KS Spycicle + Vintage Texas Ten-Gallon

http://www.tf2outpost.com/trade/28299435 - B/O of 19

Seller: http://backpack.tf/profiles/76561198021055079#!/compare/1467331200/1467417600

Buyer: http://backpack.tf/profiles/76561198167058827#!/compare/1467244800/1467417600

http://puu.sh/pNGcX/1f1b00a0f7.png

http://puu.sh/pNGe2/edb0ca9232.jpg

X = 19 (Capped by B/O)

Sale 4:

Sold for 19 keys

http://www.tf2outpost.com/trade/28140970 - B/O of 25

Seller: http://backpack.tf/profiles/76561198131054305#!/compare/1463616000/1464480000

Buyer: http://backpack.tf/profiles/76561198029534325#!/compare/1464393600/1464480000

X = 19

Sellers:

18 keys:

http://www.tf2outpost.com/trade/28299411 - 1 day, relisted from http://www.tf2outpost.com/trade/28297509

19 keys:

http://puu.sh/pNGTK/418b54971a.png

Sales at:

21

20

19 (2x)

Using the seller for the low-end

Going with 18-21