Not sure about the range but it seems to me that 5 ref rarely ever happens.

On classifieds there are many sellers for 4.66 and 4.33.

http://imgur.com/jPPd0WR sellers for 4 - 4.66

http://imgur.com/YYd9ZkG buyers for 4.33 - 4

I myself have bought the item for 4.33 and sold for 4.66 a couple of times.

Outpost:

SELLERS:

http://www.tf2outpost.com/trade/26562338 unsold for 5 ref

http://www.tf2outpost.com/trade/26560770 unsold for 5 ref

http://www.tf2outpost.com/trade/26503457 unsold for 5 ref

http://www.tf2outpost.com/trade/26501694 unsold for "bp.tf price" (5 ref)

http://www.tf2outpost.com/trade/26531742 unsold for 5.33 ref

http://www.tf2outpost.com/trade/26529360 unsold for 5 ref

http://www.tf2outpost.com/trade/26561278 probably sold (not in his bp) for 4.33 ref

http://www.tf2outpost.com/trade/26554798 unsold for 4.66 ref

http://www.tf2outpost.com/trade/26554798 sold for 4.66 ref

http://www.tf2outpost.com/trade/26533944 unsold for 4.33 ref (probably due to shitty formatting)

BUYERS:

http://www.tf2outpost.com/trade/26174155 buying for 4 ref

http://www.tf2outpost.com/trade/26145150 buying for 4.33 ref

http://www.tf2outpost.com/trade/26481269 buying for 4 ref

http://www.tf2outpost.com/trade/26190222 buying for 4 ref

http://www.tf2outpost.com/trade/26563829 buying for 4 ref

http://www.tf2outpost.com/trade/26276436 buying for 4 ref

http://www.tf2outpost.com/trade/26306976 buying for 4 ref

http://www.tf2outpost.com/trade/26352775 buying for 4 ref

My trades:

http://imgur.com/a/ATXvO Bought for 4.33, then sold for 4.66 and then bought again for 4 ref and a crate.

Sorry if I did something wrong, first time making a suggestion.