https://ip.bitcointalk.org/?u=http%3A%2F%2Fdump.bitcheese.net%2Fimages%2Faxidido%2Fbitcoin-self-cost-logscale-edited.png&t=579&c=dHbFEFVa0F5G8Q

From https://bitcointalk.org/index.php?topic=550349.40

Difficulty is clearly lagging price. You really only need logic to tell you that.