The current range is too wide. People aren't willing to pay more than 5 keys for it, but there are a lot of buyers at 4 keys + sweets. Proof is below.

Sellers:

http://www.tf2outpost.com/trade/8198276 - 6 keys, 2 week, unsold

http://www.tf2outpost.com/trade/8550516 - 5 keys + 1 ref, 2 days, unsold

http://www.tf2outpost.com/trade/8452310 - 6 days inactive, 1 offer (4 keys)

http://www.tf2outpost.com/trade/8339362 - 5 keys, sold

http://www.tf2outpost.com/trade/8467552 - 5 keys, sold

http://tf2tp.com/trade.php?trade=9059417 - 4 keys + 1 ref, sold

Buyers:

http://tf2tp.com/trade.php?trade=9134887 - 5 keys

http://www.tf2outpost.com/trade/8593245 - 4.5 keys

http://www.tf2outpost.com/trade/8498331 - 4 keys + 1 ref

http://tf2tp.com/trade.php?trade=9130301 - 4 keys + 1 ref

http://www.tf2outpost.com/trade/8249043 - 4 keys