Using last month.

Sale 1:

Sold to a bot for Midnight Whirlwind Mannrobics (15.5)

https://i.imgur.com/HdHSPsl.png - B/O of 8, according to bot.tf

Seller: https://backpack.tf/profiles/76561198386441509#!/compare/1526342400/1526428800

Buyer: https://backpack.tf/profiles/76561198424414295#!/compare/1526342400/1526515200

X = 8 (Capped by B/O)

Sales 2 & 3:

Sold for $15 and $12 on marketplace.tf

https://marketplace.tf/items/1182;5;u3004

15/1.96 = ~7.65

12/1.97 = ~6.09

X = 7.5

X = 6

Sale 4:

Sold for Pro. KS Carbonado Botkiller Knife (7)

https://i.imgur.com/HdHSPsl.png - B/O of 7 according to bot.tf

Seller: https://backpack.tf/profiles/76561198386441509#!/compare/1527379200/1527465600

Buyer: https://backpack.tf/profiles/76561198411495266#!/compare/1527379200/1527465600

X = 7

Sale 5:

Sold for 6 keys + 12 ref

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

Buyer: https://backpack.tf/profiles/76561198078209088#!/compare/1525046400/1525996800

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

X = 6.5

Sale 6:

Sold to a bot for 5 keys + 12 ref

Seller: https://backpack.tf/profiles/76561198171325534#!/compare/1525564800/1525996800

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1525564800/1525651200

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

X = 5.5

Sale 7:

Sold to a bot for 5 keys + 12 ref

Seller: https://backpack.tf/profiles/76561198354653552#!/compare/1525996800/1527638400

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1525996800/1526083200

X = 5.5

Sale 8:

Sold to a bot for 5 keys + 5 ref

Seller: https://backpack.tf/profiles/76561198170641674#!/compare/1525392000/1525996800

Buyer: https://backpack.tf/profiles/76561198386441509#!/compare/1525478400/1525564800

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

X = 5

Sale 9:

Sold to a bot for 5 keys + 5 ref

Seller: https://backpack.tf/profiles/76561198424414295#!/compare/1526342400/1526515200

Buyer: https://backpack.tf/profiles/76561198386441509#!/compare/1526428800/1526515200

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

X = 5

Sales at:

5 (2x)

5.5 (2x)

6

6.5

7

7.5

8

Plenty of bot purchases, using 5.5 as the low-end, but excluding 5.

Going with 5.5-8.