Sale 1:

Sold for 10 keys

http://www.tf2outpost.com/trade/29275434 - B/O of 11

Seller: https://backpack.tf/profiles/76561198198332539#!/compare/1500076800/1500249600

Buyer: https://backpack.tf/profiles/76561198162540967#!/compare/1499644800/1500249600

X = 10

Sale 2:

Sold for $20.99 on Marketplace.tf

https://marketplace.tf/items/147;5;u35

Couldn’t identify the item’s history.

20.99/2.05 = ~10.2

X = 10

Sale 3:

Sold for Kill-a-Watt Bootleg Base Metal Billycock (10)

No outpost

Seller: https://backpack.tf/profiles/76561198165383147#!/compare/1498435200/1498608000

Buyer: https://backpack.tf/profiles/76561198070740519#!/compare/1498521600/1498608000

X = 10

Sale 4:

Sold for Killstreak Factory New Purple Range Sniper Rifle (7) + ~3 keys in items

http://www.tf2outpost.com/trade/29218182 - B/O of 9

Seller: https://backpack.tf/profiles/76561198026129220#!/compare/1497916800/1498003200

Buyer: https://backpack.tf/profiles/76561198276443417#!/compare/1498003200/1498089600

No recent SCM sales on the killstreak purple range sniper rifle, going with the non-killstreak one:

http://steamcommunity.com/market/listings/440/Purple%20Range%20Sniper%20Rifle%20%28Factory%20New%29

X = 9 (Capped by B/O)

Sale 5:

Sold for $18 on Marketplace.tf in ~2 days

https://marketplace.tf/items/147;5;u35

https://backpack.tf/item/826347824

18/2.05 = ~8.8

X = 9

Sale 6:

Sold for 9 keys in ~2 days

No outpost

Seller: https://backpack.tf/profiles/76561198355490842#!/compare/1497916800/1498003200

Buyer: https://backpack.tf/profiles/76561198165383147#!/compare/1497916800/1498003200

X = 9

Sale 7:

Sold for Aces High Tin Topi (9) + Spec. KS Strange Medigun (~1)

http://www.tf2outpost.com/trade/29272839 - B/O of 9

Seller: https://backpack.tf/profiles/76561198045815117#!/compare/1499904000/1499990400

Buyer: https://backpack.tf/profiles/76561198106286020#!/compare/1499904000/1499990400

X = 9 (Capped by B/O)

Sale 8:

Sold for Flies Brain-Warming Wear (9) + <0.5 keys in metal

http://www.tf2outpost.com/trade/29226819 - B/O of 10

Seller: https://backpack.tf/profiles/76561198093302304#!/compare/1497225600/1497312000

Buyer: https://backpack.tf/profiles/76561198145127094#!/compare/1497225600/1497312000

Seller at 8.5 on the brain:

http://i.imgur.com/nWxdDje.png - 3 days

and aged seller at the high-end:

http://i.imgur.com/YFxiFgJ.png - 4 months

Taking 9 for the brain.

X = 9

Sale 9:

Sold for 6 keys + ~3 keys in items

http://www.tf2outpost.com/trade/29227099 - B/O of ~8.85

Seller: https://backpack.tf/profiles/76561198145127094#!/compare/1497398400/1497484800

Buyer: https://backpack.tf/profiles/76561198279985917#!/compare/1497398400/1497484800

X = 9 (Capped by B/O, rounded)

Sale 10:

Quicksold for 8 keys + 23 ref (~1)

No outpost

Seller: https://backpack.tf/profiles/76561198036254026#!/compare/1501718400/1501891200

Buyer: https://backpack.tf/profiles/76561198349633267#!/compare/1501372800/1501891200

X = 9

Sale 11:

Sold for 8 keys

http://www.tf2outpost.com/trade/28909038 - B/O of ~9.4

Seller: https://backpack.tf/profiles/76561198048156389#!/compare/1496016000/1497312000

Buyer: https://backpack.tf/profiles/76561198093302304#!/compare/1497225600/1497312000

X = 8

Sale 12:

Bulk for Steaming Chapeau

Seller: https://backpack.tf/profiles/76561198349633267#!/compare/1502064000/1502236800

Buyer: https://backpack.tf/profiles/76561198030050182#!/compare/1502150400/1502236800

Sale 13:

Sold for Stormy Storm Gym Rat

Seller: https://backpack.tf/profiles/76561198171314747#!/compare/1502150400/1502323200

Buyer: https://backpack.tf/profiles/76561198107520045#!/compare/1502064000/1502841600

Can be used on the rat.

Sellers:

8

9 (7x)

10 (3x)

No current sellers.

Buyers at 8, excluding 8.

Some sales at 9 may have quicksold, but they are far too common to be excluded.

Going with 9-10.