I'll check this because I only heard it on a news program, but iirc, a family income of $60,000 puts you in the top 10%. So if there are 2 incomes in one home each of which is $30,000, then voting Republican makes sense. However, the closer you get to the vaulted $300,000/year (i.e. the top 1%) the rewards for voting Republican increase exponentially.

Of course, in any case, voting Republican does require an absolute lack of a social conscience ;-)