People I have spoken with tend to agree that 3rd and 4th year grades are weighed more heavily, as they are based on your clinical performance, and not on "regurgitating minutia"
Best thing to do is look into different programs and see how the rank what, in order of importance with their selection for the match.
Like the other posters said...it depends...
My school weighs each 4 week rotation as 10 credits each...
for a total of 21 rotations as 210 credits....for the 3/4th years combined. I am not sure how many we had from didactic...