There isn't any defined style of "extra pale ale".
I had one from a place out east called "railroad" something. It was most certainly a wheat beer, and tasted like Oberon to me!
Summit's is more of a lighter pale ale (as in "extra pale", I guess) while sometimes "extra pale ale" means "bigger pale ale".
Since there are so many made-up interpretations of this, if you can name a commercial style that you're thinking of that the company calls "extra pale ale", we can help come up with some ideas on what they are trying to mean.