Sale 1:

Sold for Kill-a-Watt Killer’s Kabuto (34) + 1 key

Seller: https://backpack.tf/profiles/76561198024867201#!/compare/1549756800/1549843200

Buyer: https://backpack.tf/profiles/76561198197935990#!/compare/1549756800/1549843200

https://backpack.tf/item/3340349177

X = 35

Sale 2:

Sold for 32 keys + 5 ref

Seller: https://backpack.tf/profiles/76561198385963612#!/compare/1552262400/1552435200

Buyer: https://backpack.tf/profiles/76561198197935990#!/compare/1552089600/1552435200

https://backpack.tf/item/3340349177

https://i.imgur.com/mYL8dUh.png - bot.tf confirms

X = 32

Sale 3:

Sold to a bot for 27 keys + 5 ref

Seller: https://backpack.tf/profiles/76561198062749575#!/compare/1551744000/1551830400

Buyer: https://backpack.tf/profiles/76561198385963612#!/compare/1551744000/1551830400

https://backpack.tf/item/3340349177

https://i.imgur.com/mYL8dUh.png - bot.tf confirms

X = 27

Other Sales:

https://backpack.tf/item/3340349177 (all sales below)

#1

Bulk for Morning Glory Defiant Spartan

https://backpack.tf/profiles/76561198197935990#!/compare/1550275200/1551139200

https://backpack.tf/profiles/76561198316571500#!/compare/1551052800/1551139200

#2

Bulk for Duped Peace Sign Pencil

https://backpack.tf/profiles/76561198316571500#!/compare/1551139200/1551225600

https://backpack.tf/profiles/76561198062749575#!/compare/1550966400/1551225600

Sellers:

https://i.imgur.com/5HsC9ye.png

https://backpack.tf/item/3340349177 - ~37.5 keys

Sales at:

27

32

35

27 went to a quickbuying bot, excluding.

Going with 32-35.