Sale 1:

Sold for Stormy Dapper Topper (45)

http://www.tf2outpost.com/trade/28318872 - B/O of 24

Seller: http://backpack.tf/profiles/76561198061108999#!/compare/1467849600/1467936000

Buyer: http://backpack.tf/profiles/76561198008673516#!/compare/1467849600/1467936000

X = 24 (Capped by B/O)

Sale 2:

Sold for 23 keys (according to key histories on the buyer’s side)

http://www.tf2outpost.com/trade/28400746 - B/O of 22, relisted multiple times

Seller: http://backpack.tf/profiles/76561198104872710#!/compare/1470700800/1470787200

Buyer: http://backpack.tf/profiles/76561198152648165#!/compare/1470700800/1471564800

X = 23

Sale 3:

Sold for 22 keys + ~1 key in items

http://www.tf2outpost.com/trade/28290273 - B/O of 25

Seller: http://backpack.tf/profiles/76561198112750415#!/compare/1467417600/1467504000

Buyer: http://backpack.tf/profiles/76561198070549885#!/compare/1467417600/1467504000

X = 23

Sale 4:

Sold for 22 keys

No outpost

Seller: http://backpack.tf/profiles/76561198008673516#!/compare/1469059200/1469232000

Buyer: http://backpack.tf/profiles/76561198138724799#!/compare/1469232000/1469318400

X = 22

Sale 5:

Sold for 21 keys in about 1-2 days

http://www.tf2outpost.com/trade/28284579 - B/O of 22, was offered 21 by another user

Seller: http://backpack.tf/profiles/76561198080179568#!/compare/1466899200/1466985600

Buyer: http://backpack.tf/profiles/76561198112750415#!/compare/1466899200/1466985600

X = 21

Sale 6:

Quicksold for 16 keys + 10 ref

http://www.tf2outpost.com/trade/28318393 - B/O of 22

Seller: http://backpack.tf/profiles/76561198183849619#!/compare/1470441600/1470528000

Buyer: http://backpack.tf/profiles/76561198104872710#!/compare/1470355200/1470441600

X = 17

Sale 7:

Sold for Miami nights Sober Stuntsman

No outpost

Seller: http://backpack.tf/profiles/76561198081630453#!/compare/1468886400/1469318400

Buyer: http://backpack.tf/profiles/76561198069140011#!/compare/1468886400/1468972800

Most likely an outlier, current seller for 15 keys on the Stuntsman

Sellers:

24 keys:

http://www.tf2outpost.com/trade/28364064 - 3 weeks

25 keys:

http://www.tf2outpost.com/trade/28431333 - young

26 keys:

http://www.tf2outpost.com/trade/28426262 - 2 days

Sales at:

24

23 (2x)

22

21

17

Sale at 21 sold kinda quickly, and the seller had more than one person offer 21 keys for it. Excluding 21 and below.

Going with 22-24