Forth Worth can't support an NFL team. No one will go to the games. They're all Cowboys fans.
Your best bet is definitely El Paso.
I'm also curious to see the number of college football players divided by the number of NFL teams. This would give us a far better indicator of the talent pool. IMO.
Has that grown at the same rate as the general population? If not, isn't there a hole in your theory? The NFL isn't drawing players from the general population. It's drawing from the college players for the most part. DI and DII mostly if I'm not mistaken.
Alex Smith's current 9.8 YPC is one of the lowest marks in the NFL over the last 10 seasons. Only a few QBs have been worse:
Ryan Mallett (9.8), Derek Carr (9.4), Christian Ponder (9.8), Brady Quinn (9.8), Ryan Fitzpatrick (8.6), Brodie Croyle (9.7), Charlie Frye (9.7), Bruce Gradkowski (9.4), David Carr (9.2)