Sale 1:

Sold for Flies Glengarry (Suggestion at 8.5) + 1 key

http://www.tf2outpost.com/trade/29271015 - No visible B/O, nothing cached

Seller: https://backpack.tf/profiles/76561197982879578#!/compare/1500422400/1500508800

Buyer: https://backpack.tf/profiles/76561198095154703#!/compare/1500422400/1500508800

X = 10

Sale 2:

Sold for Green Confetti Elf Esteen (in-date at 10.5, seller at 9, taking 10)

http://www.tf2outpost.com/trade/29284680 - No real B/O

Seller: https://backpack.tf/profiles/76561198095154703#!/compare/1500768000/1500854400

Buyer: https://backpack.tf/profiles/76561198101378846#!/compare/1500595200/1500854400

X = 10

Sale 3:

Sold for Strange Field-Tested Liquid Asset Stickybomb Launcher (~11) + 3 keys

http://webcache.googleusercontent.com/search?q=cache:ugiTw7nkGPkJ:www.tf2outpost.com/trade/29330106+&cd=1&hl=en&ct=clnk&gl=au – B/O of 9.6

Seller: https://backpack.tf/profiles/76561198002757046#!/compare/1502841600/1502928000

Buyer: https://backpack.tf/profiles/76561198071586915#!/compare/1502841600/1502928000

X = 10 (Capped by B/O, rounded)

Sale 4:

Sold for 10 keys

No outpost

Seller: https://backpack.tf/profiles/76561198312583107#!/compare/1501200000/1501286400

Buyer: https://backpack.tf/profiles/76561198155428623#!/compare/1501200000/1501459200

X = 10

Sale 5:

Sold for 9 keys

No outpost

Seller: https://backpack.tf/profiles/76561198121830870#!/compare/1505347200/1505433600

Buyer: https://backpack.tf/profiles/76561198261900213#!/compare/1505347200/1505433600

X = 9

Sale 6:

Sold for 9 keys

http://www.tf2outpost.com/trade/29370996 - B/O of 12

Seller: https://backpack.tf/profiles/76561198098563620#!/compare/1505606400/1505692800

Buyer: https://backpack.tf/profiles/76561198040898430#!/compare/1505606400/1505692800

X = 9

Flies Glengarry:

https://backpack.tf/suggestion/59d722fccf6c757e3a264964

Sellers:

10 keys:

https://i.imgur.com/AqnKFNf.png - 17 days

12 keys:

https://i.imgur.com/m1sEW6A.png - 8 months

Sales at:

9 (2x)

10 (4x)

Going with 9-10.