@perennialloner,
Yes. And the 2 assumes preference because it uses the present tense.
I agree it is confusing as looking counter intuitive but "if you prefer" almost assumes present tense information, thus contradicting the surreptitious "if" rhetorically. It's in a no man's land between a question and supposition/guestimate, or quasi-answer.
Of course, it can be argued the preference is present but the questioner does not know it. Problem being how can one use the present in a question to which a decision is yet to be made? The scenario is hypothetical and there is a billion variables to which even a knowledge from past example might not fit the specific case/context.
I am not a native speaker, I am terrible at English, I mean really bad, but I am trying to look at pure logic alone to judge the sentence. I set how it sounds for native speakers aside.
"If you'll prefer" is the perfect Logical form, once it asks for information regarding a decision to be made in a future moment no matter how imidiatly close to present.