I don't like the 1 key gap, but well they seem to be all over between 6 and 7 keys. At the time of posting a single 6 key on classified and a handful in the 6.5 range. Also might be worth mentioning that on market they sell for around 5.5-6 keys.

6 key:

http://www.tf2outpost.com/trade/21175925 (5 keys + 7 ref)

http://www.tf2outpost.com/trade/20251727 (old trade? might be sold)

http://www.tf2outpost.com/trade/20193351 (dropped from 7, 1 month)

http://www.tf2outpost.com/trade/20899500 (1 week, takes ref?)

http://www.tf2outpost.com/trade/20956619 (1 week)

http://www.tf2outpost.com/trade/21126246

~6.5 key:

http://www.tf2outpost.com/trade/21076529 (6 key + 2 ref)

http://www.tf2outpost.com/trade/21157756 (6 key + 4 ref, mine)

http://www.tf2outpost.com/trade/20643518 (6 key + 4 ref)

http://www.tf2outpost.com/trade/21170311 (6 key + 7 ref, multiple)

7 key: don't seem to be moving

http://www.tf2outpost.com/trade/20864075 (1 week)

http://www.tf2outpost.com/trade/21121403 (2 days)

http://www.tf2outpost.com/trade/21149324

http://www.tf2outpost.com/trade/20682681 (2 weeks)

http://www.tf2outpost.com/trade/20905626 (1 week)

Buyers:

http://www.tf2outpost.com/trade/21031803 (5 keys)

http://www.tf2outpost.com/trade/18661438 (5 keys)

http://www.tf2outpost.com/trade/20162719 (5 keys)

many more buying at 5 keys