Huntsville metro isn't slowing down. It's only half the size of the Greenville, SC MSA, but they are similar, and so many things are lined up for continued crazy growth. Significant influx of industry, and with significant government contracting (Madison bests this one).
I think of car tags. You have Jefferson/Mobile/Montgomery as 1/2/3 in historical population, giving them an extra number due to their size. Now they're alphanumeric, so there's greater capacity. When Madison County (47) passed Montgomery County in total population some years ago, it was announced that there would be no change in county, which would've had a cascading effect for all counties below "M". Now that they've passed Mobile County, too, I guess they don't take 2, either. Quite a feat, given the growth on the Eastern Shore.