Using last month.

Sale 1:

Sold for 8 keys + 11 ref

Seller: https://backpack.tf/profiles/76561197983219732#!/compare/1529971200/1530057600

Buyer: https://backpack.tf/profiles/76561198071282126#!/compare/1529798400/1530057600

X = 8.5

Sale 2:

Sold for Whirlwind Balloonibouncer (Suggestion at 5.5) + 3 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1532217600/1532304000

Buyer: https://backpack.tf/profiles/76561198012988791#!/compare/1532217600/1532390400

Bot.tf confirms a B/O of 8: https://i.imgur.com/hL6m3XP.png

It states that it sold for 8 keys and 4 ref, when it sold for items. This is why bot.tf stats on untraceable sales are unreliable.

X = 8 (Capped by B/O)

Sale 3:

Sold for 8 keys + 4 ref

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1531699200/1531785600

Buyer: https://backpack.tf/profiles/76561198160861401#!/compare/1531699200/1531785600

Untraceable. Bot.tf confirms, but is unreliable. https://i.imgur.com/hL6m3XP.png

Key/metal histories below:

Keys:

https://backpack.tf/item/7004443246

https://backpack.tf/item/7004443259

https://backpack.tf/item/7004443278

https://backpack.tf/item/7004443289

https://backpack.tf/item/7004443312

https://backpack.tf/item/7004443368

https://backpack.tf/item/7004443325

https://backpack.tf/item/7004443300

Metal:

https://backpack.tf/item/7004443342

https://backpack.tf/item/7004443348

https://backpack.tf/item/7004443361

https://backpack.tf/item/7004443332

X = 8

Sale 4:

Sold for 8 keys + 4 ref?

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1531440000/1531526400

Buyer: https://backpack.tf/profiles/76561198075108450#!/compare/1531526400/1531612800

Untraceable. Bot.tf confirms, but it is unreliable. https://i.imgur.com/hL6m3XP.png

X = 8?

Sale 5:

Sold for 7 keys + 18 ref?

Seller: https://backpack.tf/profiles/76561198312583107#!/compare/1530921600/1531008000

Buyer?: https://backpack.tf/profiles/76561198203207940#!/compare/1530921600/1531094400

https://backpack.tf/item/4955393182 - Was dumped on tradeit.gg immediately after purchase by the looks of it. The seller’s end does show exactly 7 keys and 18 ref in a trade, I don’t doubt that those were the keys and metal involved.

Bot.tf confirms: https://i.imgur.com/hL6m3XP.png

X = 7.5

Sale 6:

Sold to a bot for 7 keys + ~6 ref

Seller: https://backpack.tf/profiles/76561198080253443#!/compare/1530316800/1530489600

Buyer: https://backpack.tf/profiles/76561198312583107#!/compare/1530403200/1530489600

5 ref is untraceable, but this should be enough to prove that the sale is correct. Bot.tf confirms: https://i.imgur.com/hL6m3XP.png

X = 7

Sale 7:

Sold for 7 keys + ~4 ref

Seller: https://backpack.tf/profiles/76561198105084820#!/compare/1532044800/1532131200

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1531958400/1532044800

Bot.tf confirms: https://i.imgur.com/hL6m3XP.png

X = 7

Sale 8:

Sold to a bot for 7 keys + 4 ref

Seller: https://backpack.tf/profiles/76561198071282126#!/compare/1532131200/1532390400

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1532304000/1532390400

Bot.tf confirms: https://i.imgur.com/hL6m3XP.png

X = 7

Sale 9:

Sold to a bot for 7 keys + 4 ref?

Seller: https://backpack.tf/profiles/76561198386044837#!/compare/1529884800/1530316800

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1530144000/1530230400

Most items are traceable on the seller’s end, so it should be safe to assume that it was a pure sale, no other items involved.

X = 7

Sale 10:

Sold to a bot for 7 keys + 4 ref

Seller: https://backpack.tf/profiles/76561198075108450#!/compare/1531526400/1531612800

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1531526400/1531612800

Bot.tf confirms: https://i.imgur.com/hL6m3XP.png

X = 7

Sale 11:

Sold for $29.90 on marketplace.tf

https://marketplace.tf/items/30763;5;u3004

Will end up being ~15 keys, which is way too high. Excluding.

Whirlwind Balloonibouncer:

https://backpack.tf/suggestion/5b57d692cf6c751e4636db0d

Sellers:

~8.1 keys:

https://i.imgur.com/HLZ0PWU.png

https://backpack.tf/item/5427966069

15 keys:

https://i.imgur.com/6MT4HrJ.png

https://backpack.tf/item/5864973007

40 keys:

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

https://backpack.tf/item/6895023610

51 keys:

https://i.imgur.com/407PSQx.png

https://backpack.tf/item/6046574522

Sales at:

7 (5x)

7.5

8 (2x)

8.5

And another untraceable sale at 8

Going with 7-8.5.