Sale 1:

Sold for 11 keys

Seller: https://backpack.tf/profiles/76561198159855421#!/compare/1512518400/1512604800

Buyer: https://backpack.tf/profiles/76561198185982134#!/compare/1512432000/1512864000

X = 11

Sale 2:

Sold for 9 keys + 22 ref

Seller: https://backpack.tf/profiles/76561198304138933#!/compare/1509580800/1509667200

Buyer: https://backpack.tf/profiles/76561198344919469#!/compare/1509580800/1509667200

X = 10

Sale 3:

Sold with 2 keys for Terror-Watt Madame Dixie (12.5)

http://www.tf2outpost.com/trade/29503647 - B/O of 10

Seller: https://backpack.tf/profiles/76561198043360498#!/compare/1515110400/1515196800

Buyer: https://backpack.tf/profiles/76561198133875209#!/compare/1515024000/1515196800

X = 10 (Capped by B/O)

Sale 4:

Sold for 9 keys

Seller: https://backpack.tf/profiles/76561198091502579#!/compare/1516233600/1516320000

Buyer: https://backpack.tf/profiles/76561198186884755#!/compare/1515801600/1516320000

X = 9

Sale 5: – Credit to Fish

Sold for Vivid Plasma Cadaver’s Cranium

Seller: https://backpack.tf/profiles/76561198283011895#!/compare/1509840000/1510099200

Buyer: https://backpack.tf/profiles/76561198274136188#!/compare/1509926400/1510099200

Using on the Cranium.

Sale 6:

Bulk for Scorching Titanium Pillar of Hats

Seller: https://backpack.tf/profiles/76561198094705670#!/compare/1512172800/1512345600

Buyer: https://backpack.tf/profiles/76561198014113357#!/compare/1511654400/1512345600

Sellers:

~9.5 keys:

https://i.imgur.com/LZb2n4X.png

https://backpack.tf/item/1743688282

Sales at:

9 (2x)

10 (2x)

11

Going with 9-11.