Unfortunately I don't have a linkable source for this, but the Democratic fundraising platform ActBlue gave a talk on A/B testing donation forms and it turns out that when they removed the "select card type" field, donations went -way- down. You'd think that the Law of Forms would apply (fewer fields = higher conversions), but it doesn't. Apparently people assumed that there was something wrong with the form and therefore didn't trust it (when they removed that field, they also had a huge uptick in people submitting reports of things wrong with the form).

I'm hoping someone from ActBlue's dev team sees this and can jump in. They run a lot of fascinating tests on credit card forms.