Resuggesting, I can still deem 2.1 as being too low even if 3.9's too high.

goldielocks anyone?

Sold for an Australium Pro KS Scattergun(3.5 with Overpay), 2 Keys, a Collector's Lollichop and a Strange Festive Black Box(4.5 Keys w/ overpay)(3.9 Total)

http://www.tf2outpost.com/trade/23668514

http://i.imgur.com/s8adcZ4.png

Australlium Pro KS Scattergun mini suggestion

All recent sales in the SCM(Keys = $2.49): http://steamcommunity.com/market/listings/440/Strange%20Professional%20Killstreak%20Australium%20Scattergun

$143.75

$143.72

$130.00

$125.00

$115.00

$149.49

$128.94

$149.50

$129.86

$148.34

$117.57

$128.58

$132.95

$140.00

$149.50

$149.50

$157.02

$157.02

$189.75

$169.86

$154.88

$154.99

$176.46

$170.00

$123.83

$149.50

$127.50

$127.50

$144.38

$150.00

$113.78

$155.82

$165.99

$150.00

$147.11

$145.00

$148.30

$133.09

$150.00

$141.77

$142.50

$142.50

$151.21

$151.21

$137.01

$148.03

$161.00

$115.47

The average comes out at $144.46(Roughly 58 Keys)

To support this:

http://www.tf2outpost.com/trade/24714492 Seller at 60 Keys

To support my counter:

http://www.tf2outpost.com/trade/23645789 Got offered 50 keys pure, ultimately didn't sell

http://www.tf2outpost.com/trade/23900179 The 2.1 sale sold within a day, likely a quicksell

http://www.tf2outpost.com/trade/24392163 Got a recent offer of a Burning Hard Top(2.5 with Overpay, above the current low end)

Bufu's proof(Credits to him):

Sale 1: http://www.tf2outpost.com/trade/24548569#latest

just sold for 3 buds pure http://imgur.com/fqU4JTr

Sale 2: Sold with 1 bud (14.5-15 keys at the time) for a bubbling KE (~2.85) + 8 keys(Outlier)

so the KE = the hot dogger + 7 keys

2.85x14.5 - 7 =~ 34 keys = 2.37 buds = 2.13 after overpay rounded to 2.1

http://imgur.com/mGwbppY

Bubbling KE mini - Sold with a searing plasma berliner's (~1.45) for a knifestorm medic cap (~4.3)

BP before: http://backpack.tf/profiles/76561198110137758?time=1417161600

BP after: http://backpack.tf/profiles/76561198110137758?time=1417248000

I've also gotten offers around and above 4, but I have no way of proving that. Since 3.9 is deemed too high and old, although 2.1 is just as old, 3 flat should be fine.