@sergio: Negligible at the distance I'm talking about. Admittedly it is a good 700 miles closer than Boston but it's still 900 miles away. Chicago is closer to PAX East than I am to Chicago. If you want to create a 3rd PAX for people who can't go to the other two you do it closer to the places that are 1600-2000 miles away from the other locations. That's Texas. At the very least Kansas would be okay, that's 500 miles for me.
Dallas would be best for me, I could drive to Austin in 3 hours, a flight to Kansas hopefully wouldn't be so terrible. I live 10 minutes from the airport so that'd be real convenient.
Honestly those two would be best for me but I'd also bet on them. It's the best bet for maximizing the folk who can't make it out to the North West corner or the North East corner, there's plenty of space either in Dallas or Austin, temperates will be nice and decent 70s during the Fall and early Spring, generally no snow to deal with during the Winter, do not come during the Summer, great location.
Or maybe have it somewhere that is within driving distance of 7-10 major cities like Chicago or St Louis? Even cities in Texas aren't really in driving distance of one another.