Just gonna put this out there... I've... found a correlation between Pack Art and the chances you'll get an EX.
It's just... I don't know if it's isolated or true for every box.
Thing is, me and a friend opened 5 boxes and split all the packs into 4 piles, for each different artwork.
And consistantly, there was 2 EX's pulled from Darkrai packs and 1 EX pulled from Scrafty packs.
To test the theory outside of the boxes that we got altogether, I went to a nearby Card Shop that hosts our league on Friday nights and bought the remaining Darkrai and Scrafty packs.
It wasn't a complete half of a box, being 11 packs. But I managed to pull 2 EX's (Reg and Full Art) from Darkrai packs and 1 EX (Reg) from the Scrafty packs.
Seeing my success with obtaining absolute EX's due to pack artwork, I decided to go to the local Wal-Mart and buy loads of Scrafty and Darkrai sealed single packs and see what I could pull.
The results are astounding.
From Darkrai packs, it's actually mediocre, on average pulling half an EX per ~50$ I spent.
However, Scrafty packs are an ENTIRELY different beast!
For every ~50$ that I spend on those, I usually get 2 - 4 EX's. The other day, I pulled 4 FA's from ALL of my Scrafty packs! And those FA's were: Entei, Kyogre, Darkrai, Darkrai!
But yeah, these are just my findings. Right now, since last Friday... I've pulled 20 EX's, and have spent only ~500$. ... I think.
Yeah, I know I have a problem.