At Vanderbilt, a popular trend in the last few years is to do 1st yr med-PhD (3-5 av:~3.5)-2nd-3rd-4th med. About half of last years class did it that way. I did it also, but for different reasons (complicated story including moving from overseas) and thought it was a great idea. 1st med year is not that strikingly important anyway, and 2nd year is when we do Path, Pharm, Lab Dx, Phys Dx, Neurosci.. all the major Step 1 topics (except micro&physio, but they can be easily reviewed). Knowing these things cold when entering 3rd yr is a great advantage, and also obviates the whole issue of taking all USMLE Steps within the 7-yr time-frame as required by some states (meaning those that do not exempt mudphuds).
Just my 2c.
Aleks Stanic