Proof:

Solds at 6 ref:

http://www.tf2outpost.com/trade/16505762 - Sold in 4 hours

http://www.tf2outpost.com/trade/16499134 - Sold without a bump

http://www.tf2outpost.com/trade/16475213 - 6.22 ref, sold without a bump

http://www.tf2outpost.com/trade/16484506 - 6.33 ref, sold in less than a day

http://www.tf2outpost.com/trade/16478219 - 6.33 ref, sold in 11 hours

http://www.tf2outpost.com/trade/16471043 - 6.33, sold in less than a day

http://www.tf2outpost.com/trade/16509442 - 6.33 ref, sold without a bump (same owner as above, different Black Box)

Last suggestion (kinda old but still recent enough, credit to KoDoRiN):

Solds at 1 key:

http://www.tf2outpost.com/trade/16341040 -----> http://puu.sh/5M1r1.png

http://www.tf2outpost.com/trade/16346835

http://www.tf2outpost.com/trade/16345875

http://www.tf2outpost.com/trade/16338165

http://puu.sh/5M2Zu.png

My proof:

Solds at 1 key:

http://www.tf2outpost.com/trade/16485035 - Sold in less than a day

http://www.tf2outpost.com/trade/16492880 - Sold in less than 17 hours

http://www.tf2outpost.com/trade/16496841 - Sold in 3 hours

http://www.tf2outpost.com/trade/16508243 - Sold without a bump

6.33 ref is VERY close to 1 key

Considering there are still enough available at 6 ref, even if most are quicksells, it should stay, therefore a range

0.9 keys equals ~5.85 ref which is VERY close to 6 ref

Considering there are some trades at 1 key and 1 key sells fast, and below that even faster, I think 0.9 - 1 keys is a better price right now