According to a recent study published in The Harvard Business Review Men with higher ethical standards earn less than their less ethical counterparts:

male business professionals who self-report high ethical character earn, on average, earn 3.4% less than their peers who don't report having such standards, according to an analysis of data on thousands of students by Andrew Hussey of the University of Memphis.

Interestingly, woman with higher ethical standards don't seem to suffer the same consequences, in fact differing ethical standards don't seem to have any consequences at all:

Female professionals who self-report high ethical standards receive no pay penalty, and women who said that their schooling had raised their standards received a premium averaging 5.5%.

I'm not sure how much we can read into these numbers (and I haven't read the whole study), but it seems to line up with the cliche of "nice guys finishing last." Of course, most of us would probably say that we'd prefer a higher ethical standard, to higher pay, but, maybe not everyone?