Let's start off with support proof:

Classified AS OF THE POST OF THIS SUGGESITON: http://backpack.tf/classifieds/search/id/52c941114cd7b8f8028b4568

x1 at 1.33. ( http://i.imgur.com/FdKPUDQ.png )

x1 at 1.44. ( http://i.imgur.com/zhohOYN.png )

x1 at 1.55. ( http://imgur.com/iNYvz9K )

Selling for lower than 1.66:

http://www.tf2outpost.com/trade/19940583 - "2 scrap off bp.tf price".

http://www.tf2outpost.com/trade/19938071 - 1.27.

http://www.tf2outpost.com/trade/19937823 - 1.33.

http://www.tf2outpost.com/trade/19824768 - 1.33 - 6 Days old.

http://www.tf2outpost.com/trade/19820776 - 1.33 - 6 Days old.

http://www.tf2outpost.com/trade/19932373 - 1.44 - Never bumped.

http://www.tf2outpost.com/trade/19906575 - 1.44.

http://www.tf2outpost.com/trade/19942423 - 1.55.

http://www.tf2outpost.com/trade/19923697 - 1.55 - 1 Day old.

http://www.tf2outpost.com/trade/19863000 - 1.55 - 1 Day old.

http://www.tf2outpost.com/trade/19925799 - "mid bp.tf price" - 1 Day old.

UNSOLDS for 1.66

http://www.tf2outpost.com/trade/19921075 - 1 Day old - never bumped.

http://www.tf2outpost.com/trade/19925775 - 1 Day old - never bumped.

http://www.tf2outpost.com/trade/19916411 - 1 Day old.

http://www.tf2outpost.com/trade/19922040 - 1 Day old.

http://www.tf2outpost.com/trade/19915539 - 2 Days old.

http://www.tf2outpost.com/trade/19912539 - 2 Days old.

http://www.tf2outpost.com/trade/19866339 - 4 Days old.

http://www.tf2outpost.com/trade/19755234 - 1 Week+ old.

http://www.tf2outpost.com/trade/19777528 - 1 Week+ old.

http://www.tf2outpost.com/trade/19776575 - 1 Week+ old.

http://www.tf2outpost.com/trade/19776868 - 1 Week+ old.

http://www.tf2outpost.com/trade/19710918 - 1 Week+ old.

http://www.tf2outpost.com/trade/19770282 - 1 Week+ old. - Not bumped in a day as of the post of this suggestion.

http://www.tf2outpost.com/trade/19643518 - 2 Weeks+ old.

http://www.tf2outpost.com/trade/19620250 - 2 Weeks+ old.

http://www.tf2outpost.com/trade/19371251 - 1 Month+ old.

http://www.tf2outpost.com/trade/19904238 - "backpack.tf price" - 2 Days old.

There are 1 more page on Outpost, but all are not bumped in 1+ days, so did not include.

There's also actually a lot of young trades for 1.66, some of them are reposted, but did not include.

I suggested 1.33 considering both of the 1.55 are unsolds as well.