All sales are within 30 days old.

Sale 1:

Sold for Vivid Plasma Magnificent Mongolian (Mini at 12 below)

No outpost

Seller: https://backpack.tf/profiles/76561198068783246#!/compare/1516060800/1516406400

Buyer: https://backpack.tf/profiles/76561198043683271#!/compare/1515974400/1516406400

X = 12

Sale 2:

Sold for Midnight Whirlwind Most Wanted (10)

No outpost

Seller: https://backpack.tf/profiles/76561198446905869#!/compare/1516492800/1516579200

Buyer: https://backpack.tf/profiles/76561198314160142#!/compare/1516492800/1516579200

X = 10

Sale 3:

Sold for 2 keys + ~7 keys in items

http://www.tf2outpost.com/trade/29525125 - B/O of 9

Seller: https://backpack.tf/profiles/76561198265309302#!/compare/1516320000/1516406400

Buyer: https://backpack.tf/profiles/76561198068783246#!/compare/1516060800/1516406400

The items involved re-sold instantly to quickbuying bots

X = 9

Sale 4:

Bulk

Seller: https://backpack.tf/profiles/76561198342161127#!/compare/1516233600/1516320000

Buyer: https://backpack.tf/profiles/76561198265309302#!/compare/1516147200/1516320000

Vivid Mongol Mini:

Sale 1:

Sold with ~1 key in items for Green Confetti Warhood (In-date at 13.5, 2 month old seller at 13, taking 13)

Seller: https://backpack.tf/profiles/76561198068783246#!/compare/1516406400/1516492800

Buyer: https://backpack.tf/profiles/76561198060415489#!/compare/1516406400/1516492800

X = 12

Sale 2:

Sold for 9 keys + cheap weapons

Seller: https://backpack.tf/profiles/76561198060415489#!/compare/1516492800/1516752000

Buyer: https://backpack.tf/profiles/76561198011671663#!/compare/1516665600/1516752000

Lower than buyers, excluding.

Sellers:

11 keys:

https://i.imgur.com/ku6qdmQ.png

~13.1 keys:

https://i.imgur.com/ZB5qdqe.png - 2x

15 keys:

https://i.imgur.com/yCKMfay.png - 2 months

18 keys:

http://www.tf2outpost.com/trade/29477243 - 1 month

Offers:

http://www.tf2outpost.com/trade/29516435

Sales at:

9

10

12

Going with 9-12.