Sale 1:

Sold for 10 gun mettle keys

http://www.tf2outpost.com/trade/27548170 - B/O of 10 for ~10 days

Seller: http://backpack.tf/profiles/76561198030685520?time=1450339200&compare=1450252800

Buyer: http://backpack.tf/profiles/76561198070622800?time=1450684800&compare=1450080000 (Not very helpful, this one)

X = 10

Sale 2:

Sold for Smoking Big Chief

http://www.tf2outpost.com/trade/27593941 - B/O of 11

Seller: http://backpack.tf/profiles/76561198070622800?time=1453881600&compare=1454140800

Buyer: http://backpack.tf/profiles/76561198092700900?time=1452412800&compare=1454054400 (Neither is this one)

X = 10

Big Chief History (for proof of sale)

http://www.tf2outpost.com/item/440,4542544408

Big Chief Mini:

Sold for 9 keys + ~1 key in ref and robot parts

http://www.tf2outpost.com/trade/27541816 - B/O of 10

Seller: http://backpack.tf/profiles/76561198128606394?time=1449388800&compare=1449302400

Buyer: http://backpack.tf/profiles/76561198094132328?time=1449388800&compare=1449129600

X = 10

Outpost Sellers:

http://www.tf2outpost.com/trade/27779974 - 11 keys, 2 weeks

2 sales at 10 keys

Going with 10 keys