2.5 keys is a quicksell,few sellers for 2.5 keys get an instant add most sales goes for 3.

Proof:

http://www.tf2outpost.com/trade/15309375 - 2 keys +4 ref

http://www.tf2outpost.com/trade/15308906 - going for backpack.tf's highest price range.

http://www.tf2outpost.com/trade/15307630 - sold for 4 keys and 5 ref one bump

http://www.tf2outpost.com/trade/15302659 - 3 keys

http://www.tf2outpost.com/trade/15301828 - 2 keys 3 ref

http://www.tf2outpost.com/trade/15301794 - 2 keys 5.33

http://www.tf2outpost.com/trade/15299969 - 3 keys

http://www.tf2outpost.com/trade/15298056 - 2 keys 4.66

http://www.tf2outpost.com/trade/15296825 - 3 keys

http://www.tf2outpost.com/trade/15296295 - sold 2 for 2 keys and 4 ref

http://www.tf2outpost.com/trade/15296105 - 3keys

http://www.tf2outpost.com/trade/15290950 - 3 keys another owner

http://www.tf2outpost.com/trade/15287785 - 3 keys rejected 2 keys and 4 ref

http://www.tf2outpost.com/trade/15287242 - 2 keys 4 ref

http://www.tf2outpost.com/trade/15284233 - 3keys

http://www.tf2outpost.com/trade/15282942 - 2 keys +5 ref

http://www.tf2outpost.com/trade/15282203 - 3keys

http://www.tf2outpost.com/trade/15280466 - selling for 3 keys rejected 2 keys and 4 ref

http://www.tf2outpost.com/trade/15279221 - someone wanna buy it for 3 keys in comments

http://www.tf2outpost.com/trade/15277818 - 3keys another owner

http://www.tf2outpost.com/trade/15275020 - 3keys

http://www.tf2outpost.com/trade/15274550 - 3keys

http://www.tf2outpost.com/trade/15273673 - 3keys

http://www.tf2outpost.com/trade/15271570 - 3keys

http://www.tf2outpost.com/trade/15269237 -3keys

http://www.tf2outpost.com/trade/15266682 - 3keys