If anything, I might expect the opposite to be true in this context.

Well consider the hypothetical I proposed:

suppose you are having a Socratic dialogue with someone who holds irrational belief X. Instead of simply laying out your argument, you ask the person whether he agrees with Proposition Y, where Proposition Y seems pretty obvious and indisputable. Our rational person might quickly and easily agree or disagree with Y. Whereas our irrational person needs to think more carefully about Y; decide whether it might undermine his position; and if it does, construct a rationalization for rejecting Y. This difference in thinking might be measured in terms of reaction times.

See what I mean?

I do agree that in other contexts, self-deception might require less thought. e.g. spouting off the socially preferable answer to a question without really thinking about what the correct answer is.

It'd definitely be interesting to hook someone up to a polygraph or EEG and have them take the Crowne-Marlowe Scale, though.

Yes.