This is a very difficult question. Yes, the GPAs and MCATs are often higher, but that is more from self-selection, I personally believe. There are often less applicants for the seats available. In general, I think the main extra difficulty part comes from doing the undergraduate research. If you've got that out of the way, you're nearly set. That's not counting the actual application process which certainly is MUCH more difficult than straight MD, at least twice as difficult. You're going to have much more secondary paperwork and many more interviews. The good news is...a great deal of the paperwork and interview questions will be very similiar.