Sale 1:

Sold for Stormy Mongolian (9) + Pro. KS Iron Bomber Kit (~3)

http://www.tf2outpost.com/trade/29209370 - B/O of 11, Mindacos was brokering for Fish.

Seller: https://backpack.tf/profiles/76561198044195191#!/compare/1500854400/1500940800

Buyer: https://backpack.tf/profiles/76561198302590706#!/compare/1500940800/1501027200

X = 11 (Capped by B/O)

Sale 2:

Sold for Aces High Base Metal Billycock (11) + 3 festivizers (~3)

http://www.tf2outpost.com/trade/29225179 - B/O of 10

Seller: https://backpack.tf/profiles/76561198097135729#!/compare/1497225600/1497312000

Buyer: https://backpack.tf/profiles/76561198148069248#!/compare/1497225600/1497312000

X = 10 (Capped by B/O)

Sellers:

10 keys:

http://i.imgur.com/V7Tqeok.png - 25 days

http://www.tf2outpost.com/trade/29327307

And another one on marketplace for around 10 keys worth:

https://marketplace.tf/partneritem?sku=30005;5;u35&attrib=bp

Sales at:

10

11

Going with 10-11.