Sale 1:

Sold for 5 keys

Seller: https://backpack.tf/profiles/76561198358932637#!/compare/1527033600/1527120000

Buyer: https://backpack.tf/profiles/76561198204380849#!/compare/1526860800/1527120000

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

X = 5

Sale 2:

Sold for Cyclone Oblooterated (Suggestion at 4) + ~0.5 keys in items

No outpost

Seller: https://backpack.tf/profiles/76561198173794751#!/compare/1525478400/1525564800

Buyer: https://backpack.tf/profiles/76561198264400158#!/compare/1525392000/1525478400

X = 4.5

Sale 3:

Sold to a buy order for $9.05 on marketplace.tf

https://marketplace.tf/items/1117;5;u3004

9.05/1.97 = ~4.6

X = 4.5

Sale 4:

Sold to a bot for 3 keys + 5 ref

Seller: https://backpack.tf/profiles/76561198253485116#!/compare/1526515200/1526601600

Buyer: https://backpack.tf/profiles/76561198358932637#!/compare/1526515200/1526601600

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

X = 3

Cyclone Oblooterated:

https://backpack.tf/suggestion/5b0e481f44325a277d5672b2

Sellers:

5 keys:

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

https://backpack.tf/item/6421465228

https://backpack.tf/item/3315808306

6 keys:

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

https://backpack.tf/item/4114139941

10 keys:

https://i.imgur.com/0LqIQce.png

https://backpack.tf/item/5081957915

Sales at:

3

4.5 (2x)

5

Sales below 5 are too common to ignore. Excluding 3 and keeping 4.5.

Going with 4.5-5.