Using last month.

Sale 1:

Sold for ~8 keys in items

http://www.tf2outpost.com/trade/29600836 - B/O of 8

Seller: https://backpack.tf/profiles/76561198071082937#!/compare/1525392000/1525564800

Buyer: https://backpack.tf/profiles/76561198148815032#!/compare/1517616000/1525564800

Some items in the buyer’s end were involved too, despite histories not matching. If you look at the key and the metal in the seller’s end, it’ll match with the next person in the bill’s hat history, so it’s highly likely that it sold before it was scanned in their backpack.

X = 8

Sale 2:

Sold with Gift Bringer (~0.5) for Whirlwind Yeti Smash (7)

Seller: https://backpack.tf/profiles/76561198148815032#!/compare/1525564800/1525651200

Buyer: https://backpack.tf/profiles/76561198060802427#!/compare/1525651200/1525737600

X = 6.5

Sellers:

20 keys:

https://i.imgur.com/8ZgqWi0.png

https://backpack.tf/item/3902480434

https://backpack.tf/item/6261775525

25 keys:

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

https://backpack.tf/item/4562969781

Offers:

http://www.tf2outpost.com/trade/29620696

http://www.tf2outpost.com/trade/29648276

Sales at:

6.5

8

Going with 6.5-8.