According to Heather Boushe, they don't gain this even if they greatly reduce racism. The point that seems to be made is that in the short and medium term whites income is greater than it would be if racism was greatly lowered.
(She also make this point about sexism, but I think the sexism part is easily refutable. Most men live in households with women wage earners; generally with shared bank accounts. In these cases men do *NOT* benefit financially even in the immediate term from sexism.)
In terms of racism, if Boushe is wrong, I'd like to see someone show the mistake in her numbers -- rather than just trying to refutes facts (facts which of course may be wrong) with Marxist theory. [This is not an argument against Marxist theory, but against trying to refute factual claims by purely theoretical arguments.