Sale 1:

Sol for 6 keys

Seller: https://backpack.tf/profiles/76561198357046243#!/compare/1522972800/1523059200

Buyer: https://backpack.tf/profiles/76561198010578573#!/compare/1522886400/1523059200

Bot.tf confirms: https://i.imgur.com/PO8BKVK.png

X = 6

Sale 2:

Sold for 5 keys + 13.88 ref

Seller: https://backpack.tf/profiles/76561198357046243#!/compare/1520812800/1520899200

Buyer: https://backpack.tf/profiles/76561198198217295#!/compare/1520726400/1520899200

Bot.tf confirms: https://i.imgur.com/PO8BKVK.png

X = 5.5

Sale 3:

Sold to a quickbuyer for 5 keys

Seller: https://backpack.tf/profiles/76561198071620782#!/compare/1521676800/1521763200

Buyer: https://backpack.tf/profiles/76561198048851745#!/compare/1521676800/1521763200

X = 5

Sale 4:

Sold for 5 keys

Seller: https://backpack.tf/profiles/76561198097235512#!/compare/1523318400/1523404800

Buyer: https://backpack.tf/profiles/76561198269636307#!/compare/1523318400/1523404800

X = 5

Sale 5:

Sold for 5 keys + cheap items

Seller: https://backpack.tf/profiles/76561198269636307#!/compare/1523318400/1523404800

Buyer: https://backpack.tf/profiles/76561198172136521#!/compare/1523318400/1523404800

One of the keys were used on the Aces Cyborg: https://backpack.tf/profiles/76561198173902417#!/compare/1523404800/1523491200 (first one)

X = 5

Sale 6:

Sold for a lot of items

Seller: https://backpack.tf/profiles/76561198816806580#!/compare/1523059200/1523404800

Buyer: https://backpack.tf/profiles/76561198385366296#!/compare/1523318400/1523404800

Best to not get an exact number out of this sale.

Sellers:

6 keys:

https://i.imgur.com/PqAZ4Bc.png

https://backpack.tf/item/2847805091

7 keys:

https://i.imgur.com/23ADpvJ.png

https://backpack.tf/item/2724997571

~7.05 keys:

https://i.imgur.com/XOnHz1f.png

https://backpack.tf/item/6478021014

https://backpack.tf/item/2823270880

9 keys:

https://i.imgur.com/IyNs7D5.png

https://backpack.tf/item/2858442594

10 keys:

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

https://backpack.tf/item/2954150622

16 keys:

https://i.imgur.com/baORD5D.png

https://backpack.tf/item/3996866552

Sales at:

5 (3x)

5.5

6

One of the sales at 5 went to a quickbuyer, but given that there are no current quickbuyers at 5, and the amount of sales at 5, it should stay in the range.

Going with 5-6.