Sellers as low as 5.33 ref and buyer offers as high as 6 ref.

Proof:

Classifieds one unsold at 1.25 keys, many unsold at 1.5 keys http://backpack.tf/classifieds/search/6010/6/0

No offers above a key after 1 week http://www.tf2outpost.com/trade/9458141

Selling for 5.33 ref:

1 willing buyer http://www.tf2outpost.com/trade/9603350

No adds http://www.tf2outpost.com/trade/9652373

Selling for 1 key + 1.11 ref:

7 hrs http://www.tf2outpost.com/trade/9668584

Selling for 5.66 ref:

1 day http://www.tf2outpost.com/trade/9648493

Unsold for 6 ref:

2 days http://www.tf2outpost.com/trade/9617996

Unsold for 1.5 keys (1 key + 2 ref / 6.33 ref):

4 weeks http://www.tf2outpost.com/trade/8964407

2 weeks http://www.tf2outpost.com/trade/9310370

1 week http://www.tf2outpost.com/trade/9395627 the reason for the 6 ref high range

6 days http://www.tf2outpost.com/trade/9509291

5 days http://www.tf2outpost.com/trade/9526354

5 days http://www.tf2outpost.com/trade/9540079

4 days http://www.tf2outpost.com/trade/9567968

3 days http://www.tf2outpost.com/trade/9592997

1 day http://www.tf2outpost.com/trade/9637606

1 day http://www.tf2outpost.com/trade/9637899

1 day http://www.tf2outpost.com/trade/9640471

1 day http://www.tf2outpost.com/trade/9650135 Gave up after a day

17 hrs http://www.tf2outpost.com/trade/9654907 Guy who said "Added" probably offered lower because the seller still has it and it's the same guy who offered on all of the other trades

10 hrs http://www.tf2outpost.com/trade/9665126

7 hrs http://www.tf2outpost.com/trade/9669210

5 hrs http://www.tf2outpost.com/trade/9673050