Using last month.

Sale 1:

Sold for 8 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1525824000/1525910400

Buyer: https://backpack.tf/profiles/76561198057468576#!/compare/1525824000/1525910400

Bot.tf confirms: https://i.imgur.com/wmgrbLf.png

X = 8

Sale 2:

Sold for 8 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1527292800/1527379200

Buyer: https://backpack.tf/profiles/76561198131478921#!/compare/1527292800/1527379200

Bot.tf confirms: https://i.imgur.com/wmgrbLf.png

X = 8

Sale 3:

Sold for 8 keys

Seller: https://backpack.tf/profiles/76561198002757046#!/compare/1525996800/1526083200

Buyer: https://backpack.tf/profiles/76561198071737757#!/compare/1525996800/1526083200

X = 8

Sale 4:

Sold to a bot for 7 keys + 5 ref

Seller: https://backpack.tf/profiles/76561198061099804#!/compare/1525737600/1525824000

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1525737600/1525824000

Bot.tf confirms: https://i.imgur.com/wmgrbLf.png

X = 7

Sale 5:

Sold to a bot for 6 keys + 15 ref

Seller: https://backpack.tf/profiles/76561198057468576#!/compare/1527120000/1527206400

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1527120000/1527206400

Bot.tf confirms: https://i.imgur.com/wmgrbLf.png

X = 6.5

Sellers:

10 keys:

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

https://backpack.tf/item/3020955750

https://backpack.tf/item/3817761852

~10.5 keys:

https://i.imgur.com/DCaK8uO.png

https://backpack.tf/item/6347593706

12 keys:

https://i.imgur.com/s1NyYwp.png

https://backpack.tf/item/2863025922

Offers:

http://www.tf2outpost.com/trade/29645541

Sales at:

6.5

7

8 (3x)

6.5 seems kinda low, excluding.

Going with 7-8.

https://backpack.tf/profiles/76561198080275559#!/compare/1527984000/1528156800

https://backpack.tf/profiles/76561198305676157#!/compare/1528070400/1528156800

sold to a bot for ~6.5 keys

being re-sold for ~8

https://i.imgur.com/9PFXpFe.png

https://backpack.tf/item/4453254802

tempted to do 6.5-8 now