It's good that you emphasize what you want "personally." This way you can reply to the 4/6 question without sounding like you are making a blanket statement of fact, which may not go over well.How about the "why do you want to attend a 4 year program over a 6 year program (or vice versa)?"
I personally want to attend a 6 year program because I find med school attractive and I like the extra training. Is that enough? What the best way of saying that without offending anyone?