In the US, the different denominations of Christianity are actually classifiable by socio-economic breakdown. Also, I would assume that in the South, mixed White/Black churches would be very uncommon. This ain't Canada by a longshot.
Upper Class tends to be predominated by Episcopalians.
Upper-Middle Class follows with Unitarian and Presbyterian.
Lower-Middle Class consists mostly of Lutherans and Methodists, followed by Baptists near the Lower Class scale.
I don't know where the different movements (Fundamentalist, Pentecostal, Charismatic, etc) lie on the scale, but there may be more than simple geographical correlation with these movements and the corresponding socio-economic distribution.