http://backpack.tf/classifieds/search/id/528305b44dd7b81f2c8b4567 (1 at 3, lots at 4, 2 at 4.5)

Unsold:

4.5 keys:

http://www.tf2outpost.com/trade/15807116 (<1 day)

http://www.tf2outpost.com/trade/15804784 (<1 day)

http://www.tf2outpost.com/trade/15806855 (<1 day)

Selling:

4.33 keys:

http://www.tf2outpost.com/trade/15809219 (<1 day)

http://www.tf2outpost.com/trade/15794201 (1 day)

4 keys:

http://www.tf2outpost.com/trade/15803558 (<1 day)

3.66 keys:

http://www.tf2outpost.com/trade/15754390 (2 days)

3.33 keys:

http://www.tf2outpost.com/trade/15780625 (1 day)

3 keys:

http://www.tf2outpost.com/trade/15795666 (1 day)

http://www.tf2outpost.com/trade/15778891 (1 day)

Less than 2 pages on Outpost.

So, there's actually more sellers at 3 keys than 4 keys on Outpost. I think 3 keys should be in the range, however 4.5 shouldn't. Keeping 4.33 in the range as there's still sellers and I can't prove it doesn't sell.

Thanks for voting : )