Resuggesting

Very old price:

Sold for anti freeze hoodie (6.7):

http://www.tf2outpost.com/trade/16795523

Sold for cloud 9 cold killer + specialized scattergun fabricator (6.5 because seller's B/O is at that):

http://www.tf2outpost.com/trade/16647745

Blind Polar Bear's part:

http://www.tf2outpost.com/trade/16335334 - moon bonnet - 1 year old price :/

http://www.tf2outpost.com/trade/16279036 - arcana yellow belt, but b/o of 6

There's the sale of the dome which you are pricing at ~4.5 and a few quicksells at 5 and a lot of trades for hats with no price or an outdated one.....

I think 6-6.7 would be better. I'd be okay calling the 4.5 and 5 outliers.