In my opinion this shouldn't be a range since the below 4 keys trades are so hard to get, but ok, obviously if there is the slightest possibility to get a part at below 4 keys a range is needed.

Copy pasta of old suggestion; new links marked.

Very few on Outpost; nearly everyone wants 5 keys.

You can forget Bazaar; no actively bumped trades there.

SELLERS:

Anything below 4 keys is more or less quicksale.

http://backpack.tf/classifieds/?item=Strange%20Part:%20Damage%20Dealt&quality=6&tradable=1&craftable=1

No sellers below 5 keys at the moment of posting.

Sold below 4 keys:

http://www.tf2outpost.com/trade/22329235 - 3 keys; sold without bump

http://www.tf2outpost.com/trade/22302108 - 3 keys; sold without bump

http://www.tf2outpost.com/trade/22350556 - 3 keys; sold without bump (!NEW!)

http://www.tf2outpost.com/trade/22349331 - 3 keys; sold without bump (!NEW!)

http://www.tf2outpost.com/trade/22349019 - 3 keys; sold without bump (!NEW!)

http://www.tf2outpost.com/trade/22348513 - 3 keys; sold within 30 minutes (!NEW!)

http://www.tf2outpost.com/trade/22328896 - 3 keys; sold within 41 minutes

http://www.tf2outpost.com/trade/22310414 - 3 keys 4 hours

http://www.tf2outpost.com/trade/22305771 - 3 keys (check backpack)

http://tf2tp.com/trade.php?trade=10249167 - 3 keys (check backpack) (!NEW!)

http://www.tf2outpost.com/trade/22316275 - 3 keys + 3 ref; sold 2 within 13 hours

http://www.tf2outpost.com/trade/19554229 - 3 keys + 2.22 ref

Sellers below 4 keys:

http://www.tf2outpost.com/trade/22348068 3.5 keys; good luck getting that (!NEW!)

Sold at 4 keys:

http://i.imgur.com/fUAbx1m.png

http://i.imgur.com/QnJtEa6.png

http://i.imgur.com/pZ5sOUZ.png

http://www.tf2outpost.com/trade/22353162 (!NEW!)

http://www.tf2outpost.com/trade/22349195 (!NEW!)

http://www.tf2outpost.com/trade/21576492 (check history of the part)

http://bazaar.tf/trade/950744 (incredibly old proof though)

Sellers at ~4 keys:

http://www.tf2outpost.com/trade/21576492 - 4 keys (trying to restock constantly; only 1 part left though)

http://www.tf2outpost.com/trade/22249979 - 4 keys + 2 ref (only 1 part)

Other proof:

http://www.tf2outpost.com/trade/21894594 Was offered 4 keys

BUYERS:

http://bazaar.tf/trade/989833 - 3 keys

http://www.tf2outpost.com/trade/21228967 - 3 keys

http://www.tf2outpost.com/trade/22295099 - 3 keys

http://www.tf2outpost.com/trade/18108417 - 3 keys

http://www.tf2outpost.com/trade/21781306 - 3 keys

http://www.tf2outpost.com/trade/21359505 - 3 keys (that guy who is trying to restock constantly)

Bought:

http://www.tf2outpost.com/trade/22289517 - 4 keys

Feedback appreciated.