Sale 1:

Sold for 3 keys + 20 ref

Seller: https://backpack.tf/profiles/76561198335791307#!/compare/1541808000/1541894400

Buyer: https://backpack.tf/profiles/76561198308423138#!/compare/1541894400/1541980800

https://backpack.tf/item/6974804647

https://i.imgur.com/8cRuEFf.png - confirmed by bot.tf

X = 3.5

Sale 2:

Sold for 3 keys + 14 ref

Seller: https://backpack.tf/profiles/76561198312583107#!/compare/1542758400/1542844800

Buyer: https://backpack.tf/profiles/76561198054033879#!/compare/1542758400/1542844800

https://backpack.tf/item/6401000814

https://i.imgur.com/8cRuEFf.png - confirmed by bot.tf

X = 3.5

Sale 3:

Sold for 3 keys + 19.66 ref

Seller: https://backpack.tf/profiles/76561198312480435#!/compare/1542153600/1542326400

Buyer: https://backpack.tf/profiles/76561198096186958#!/compare/1542326400/1542412800

https://backpack.tf/item/4445072817

https://i.imgur.com/8cRuEFf.png - confirmed by bot.tf

X = 3.5

Sale 4:

Sold for 3 keys

Seller: https://backpack.tf/profiles/76561198193651775#!/compare/1544400000/1544486400

Buyer: https://backpack.tf/profiles/76561198383491727#!/compare/1544400000/1544486400

https://backpack.tf/item/2799161470

X = 3

Other Sales:

https://backpack.tf/item/6974804647 (#1)

https://backpack.tf/item/6928937546 (#2)

https://backpack.tf/item/6490857702 (#3)

https://backpack.tf/item/6401000814 (#4-7)

https://backpack.tf/item/4445072817 (#8)

https://backpack.tf/item/3394514972 (#9)

https://backpack.tf/item/3394514972 (#10)

https://backpack.tf/item/2811582880 (#11)

https://backpack.tf/item/4784258270 - marketplace

https://backpack.tf/item/6588369212 - gambled

#1

Untraceable

https://backpack.tf/profiles/76561198308423138#!/compare/1544140800/1544227200

https://backpack.tf/profiles/76561198382290208#!/compare/1544140800/1544227200

Later transferred to bot owner.

#2

Untraceable

https://backpack.tf/profiles/76561198311498888#!/compare/1542153600/1542240000

https://backpack.tf/profiles/76561198834758731#!/compare/1541376000/1542585600

The rest of the history appears to be just gambling.

#3

Sold for some strange festivized sniper rifle

https://backpack.tf/profiles/76561198089955737#!/compare/1544140800/1544227200

https://backpack.tf/profiles/76561198047868396#!/compare/1543104000/1544227200

Not worth looking into

#4

Untraceable

https://backpack.tf/profiles/76561198054033879#!/compare/1543622400/1543881600

https://backpack.tf/profiles/76561198335791307#!/compare/1543536000/1543622400

https://i.imgur.com/8cRuEFf.png – Labelled as a 3 key and 1 ref purchase here

#5

Untraceable

https://backpack.tf/profiles/76561198335791307#!/compare/1543622400/1543708800

https://backpack.tf/profiles/76561198860981388#!/compare/1541721600/1543708800

https://i.imgur.com/8cRuEFf.png – Labelled as a 3 key + 19.66 ref sale here

#6

Bulk for Planets Counterfeit Billycock

https://backpack.tf/profiles/76561198860981388#!/compare/1541721600/1543708800

https://backpack.tf/profiles/76561198159552857#!/compare/1543622400/1543708800

#7

Sold for cheap items

https://backpack.tf/profiles/76561198159552857#!/compare/1543795200/1543881600

https://backpack.tf/profiles/76561198359147197#!/compare/1543622400/1543795200

Not worth looking into.

#8

Untraceable

https://backpack.tf/profiles/76561198096186958#!/compare/1542326400/1542412800

https://backpack.tf/profiles/76561198048851745#!/compare/1542326400/1542412800

#9

Untraceable

https://backpack.tf/profiles/76561198115122164#!/compare/1542240000/1542672000

https://backpack.tf/profiles/76561198182817854#!/compare/1484870400/1542672000

#10

Untraceable

https://backpack.tf/profiles/76561198312583107#!/compare/1543708800/1543795200

https://backpack.tf/profiles/76561198066330410#!/compare/1543536000/1543795200

#11

Untraceable

https://backpack.tf/profiles/76561198088764747#!/compare/1543881600/1543968000

https://backpack.tf/profiles/76561198335791307#!/compare/1543881600/1543968000

https://i.imgur.com/8cRuEFf.png – Labelled as 3 keys + 1 ref

And 2 sales on marketplace that are gonna be too high to use here:

https://marketplace.tf/items/1114;5;u3009

Sellers:

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

https://backpack.tf/item/4542940884 - ~3.33 keys

https://backpack.tf/item/4445072817 - ~3.38 keys

https://backpack.tf/item/3394514972 - ~3.38 keys

https://backpack.tf/item/2811582880 - ~3.47 keys

https://backpack.tf/item/5792769798 - 4 keys

https://backpack.tf/item/2799161470 - ~6.6 keys

Sales at:

3

3.5 (3x)

Keeping 3 due to the large amount of sales recorded at 3 on bot.tf.

Going with 3-3.5.