Using last month.

Sale 1:

Sold for 7 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1534636800/1534723200

Buyer: https://backpack.tf/profiles/76561198116779194#!/compare/1534636800/1534723200

https://backpack.tf/item/6732724459

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

X = 7

Sale 2:

Sold with 1 key in items for 5 keys + ~2.5 keys in items

No outpost

Seller: https://backpack.tf/profiles/76561198126489745#!/compare/1536364800/1536537600

Buyer: https://backpack.tf/profiles/76561198345866725#!/compare/1536278400/1536537600

https://backpack.tf/item/6591959120

X = 6.5

Sale 3:

Sold for 6 keys + 20 ref

Seller: https://backpack.tf/profiles/76561198312583107#!/compare/1534723200/1534809600

Buyer: https://backpack.tf/profiles/76561198103050565#!/compare/1534809600/1535155200

https://backpack.tf/item/5047363773

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

X = 6.5

Sale 4:

Sold to a bot for 5 keys

Seller: https://backpack.tf/profiles/76561198323281330#!/compare/1536019200/1536105600

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1536019200/1536105600

https://backpack.tf/item/6291050325

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

X = 5

Other Sales:

https://backpack.tf/item/6732724459 (#1)

https://backpack.tf/item/6591959120 (#2)

https://backpack.tf/item/5374475099 (#3)

https://backpack.tf/item/6291050325 - Not unusual at the time of the sales

#1

Gifted

https://backpack.tf/profiles/76561198116779194#!/compare/1534723200/1534809600

https://backpack.tf/profiles/76561198058877862#!/compare/1517356800/1536796800

#2

Sold for Mega Strike Yeti Punch + ~2 keys in items

No outpost

https://backpack.tf/profiles/76561198254918432#!/compare/1535500800/1535587200

https://backpack.tf/profiles/76561198126489745#!/compare/1528502400/1535587200

Not using without a B/O.

#3

Gifted

https://backpack.tf/profiles/76561198223191956#!/compare/1534550400/1534896000

https://backpack.tf/profiles/76561198247640596#!/compare/1534636800/1534896000

There’s another bot.tf purchase at 5 ref, but it is untraceable to the point that the history can’t be found.

https://bot.tf/stats/item?def=30762&q=5&ef=Showstopper&craft=1&aus=0&ks=0

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

https://backpack.tf/profiles/76561198295122993#!/compare/1536796800/1536883200

Sellers:

https://i.imgur.com/KAU1lBV.png

https://backpack.tf/item/5796507526 - ~6.56 keys

https://backpack.tf/item/5135201561 - ~6.82 keys

https://backpack.tf/item/6291050325 - 7 keys

https://backpack.tf/item/5378129403 - 12 keys

https://backpack.tf/item/4952973092 - 13 keys

Sales at:

5

6.5 (2x)

7

7 is too high, given the 2 months unsold at ~6.82 keys, and nearly 1 month unsold at ~6.56 keys. Excluding 7.

Going with 5-6.5