The number of sellers at 17 keys in classies is too many to ignore.

8th Aussie Suggestion.

Seller at 17 keys

http://www.tf2outpost.com/trade/27545022 (1 day)

Seller at 17 keys 10 ref

http://www.tf2outpost.com/trade/27534783 (3 days, spec ks)

Seller at 17 keys 14 ref

http://www.tf2outpost.com/trade/27540213 (1 day)

Sellers at 18 keys

http://www.tf2outpost.com/trade/27548269 (young, spec ks)

http://www.tf2outpost.com/trade/27544408 (1 day, ks)

http://www.tf2outpost.com/trade/27528868 (4 days)

http://www.tf2outpost.com/trade/27522494 (5 days)

http://www.tf2outpost.com/trade/27479630 (1 week)

http://www.tf2outpost.com/trade/27440162 (2 weeks, spec ks)

Classifieds

Sellers:

http://i.imgur.com/XlXXY2i.png

http://i.imgur.com/bA58noj.png

Buyers:

http://i.imgur.com/Vqx8TwL.png

Conclusion

17 keys seems to be new selling point, 18 keys is difficult to sell, even with killstreaks. Proof or feedback will be appreciated.