Sales supporting the range:

Sale 1:

Sold for 30 keys

http://www.tf2outpost.com/trade/27797055 - No B/O

Seller: http://backpack.tf/profiles/76561198095072235/#!/compare/1454486400/1454572800

Buyer: http://backpack.tf/profiles/76561198025175889/#!/compare/1454486400/1457164800

This key was not involved in the trade: http://backpack.tf/item/4443696363

Sale 2:

Sold for a Max's Head

No outpost link available

Seller: http://backpack.tf/profiles/76561198085342408/#!/compare/1455782400/1456041600

Buyer: http://backpack.tf/profiles/76561198067289381/#!/compare/1456041600/1456214400

X = 29.5

Rounding to 30

Sale 3:

Sold for:

Green Confetti Thirst Blood + Black Essential Accessories

http://www.tf2outpost.com/trade/27656144 - B/O of 31, buyer states his offer here also

Seller: http://backpack.tf/profiles/76561198067478696/#!/compare/1453190400/1453622400

Buyer: http://backpack.tf/profiles/76561198042479716/#!/compare/1453190400/1453622400

X = 26 + 1

X = 27

Sale 4:

Sold for:

Strange Festive Pro. KS Stickybomb Launcher (15)

Strange Festive Pro. KS Black Box (12)

Strange Festive Buff Banner (2)

Green Confetti Coupe D'isaster (?)

http://www.tf2outpost.com/trade/27733335 - B/O of 33.5 keys (Rounding down to 33, cannot exceed B/O)

Seller: http://backpack.tf/profiles/76561198042479716/#!/compare/1455523200/1455782400

Buyer: http://backpack.tf/profiles/76561198082869766/#!/compare/1455523200/1455782400

X = 15 + 12 + 2 + ?

X = 29 + ?

X = 33

As this is capped by the B/O, the price here would only change if the Coupe Disaster was less than 4 keys, which is impossible, because there are buyers for at least 7-8 keys

Sale 5:

Sold for Miami Nights Large Luchadore + 1 key in items

No outpost link available

Seller: http://backpack.tf/profiles/76561198082869766/#!/compare/1455782400/1457078400

Buyer: http://backpack.tf/profiles/76561198200886517/#!/compare/1455782400/1455955200

X = 22.5 + 1

X = 23.5

Rounding to 24

Sale 6:

Sold for Stormy Storm Fur-lined Fighter + Circling Heart Mongolian

http://www.tf2outpost.com/trade/27570414 - B/O of 31 keys

Seller: http://backpack.tf/profiles/76561198055104415/#!/compare/1455350400/1455436800

Buyer: http://backpack.tf/profiles/76561198055293824/#!/compare/1455350400/1455523200

X = 17 + 15

X = 32

Capped by B/O of 31

Mongolian Mini:

Sale 1:

Sold for 15 keys

http://www.tf2outpost.com/trade/27833379 - B/O of 15

Seller: http://backpack.tf/profiles/76561198107520045/#!/compare/1455868800/1455955200

Buyer: http://backpack.tf/profiles/76561198049748674/#!/compare/1455955200/1456300800

Some of the key histories don't show the buyer in it, there is a good chance that the buyer acquired those keys then got rid of them before their backpack got scanned

X = 15

Only reason I didn't turn this into a suggestion was due to the unsold at 4 months for 14 keys, and I wasn't sure what price I would've had to suggest at. Either way, it wouldn't affect this suggestion here, due to the B/O

Additional sales:

Sale 7:

Sold for Kill-a-Watt Tam O' Shanter + Buds + 1 key in items

http://www.tf2outpost.com/trade/27873724 - B/O of 35

Seller: http://backpack.tf/profiles/76561198200886517/#!/compare/1455955200/1456041600

Buyer: http://backpack.tf/profiles/76561198085342408/#!/compare/1455782400/1456041600

Should be used to update the Tam O' Shanter, due to the lack of proper sales on the thing

X = 17 + 15

X = 32

Capped at 31

Sale 8:

Possible bulk for Duped Circling Heart Texas Ten Gallon

Seller: http://backpack.tf/profiles/76561198014463673/#!/compare/1450771200/1450857600

Cannot find buyer

Sale 9:

Sold with Killstreak Australium Rocket Launcher for some CS:GO knife Brokering? http://www.tf2outpost.com/trade/27712882

http://www.tf2outpost.com/trade/27677859

Seller: http://backpack.tf/profiles/76561198145465595/#!/compare/1452326400/1452844800

Buyer: http://backpack.tf/profiles/76561198069884729/#!/compare/1452758400/1452931200

The knife: http://www.tf2outpost.com/trade/27715201 (The other items most likely weren't involved)

Sale 10:

No clue what it sold for

http://www.tf2outpost.com/trade/27712882 - B/O of 30 keys

Seller: http://backpack.tf/profiles/76561198069884729/#!/compare/1452931200/1453190400

Buyer: http://backpack.tf/profiles/76561198096703310/#!/compare/1453017600/1453104000

Sales at:

33

31

30 (pure)

30 (max's)

27

24

Going with 30-31, as it seems to be a pretty common trading point.