ok, well it also depends what uni you want to do med at. UNSW only offers med as undergrad (with the specialisations being postgrad), while Syd Uni only offers it as postgrad. Have you considered other unis? (Their entry requirements aren't as harsh as these 2 unis).
Yes, you would have 2 degrees in that 7 years, but thats if you want to persevere with a B Med Sci for 3 years (obviously not what you're really interested in) -and assume that you'll be able to get into the postgrad (I'm sure the competitions tough), whereas with the transfer, you'd be in there from 2nd year learning the real stuff that you're interested in
So, I'm guessing you sat the UMAT but don't feel too confident? Remember that B Med Sci is still around a 93.something UAI, some rural students got into UNSW Med last year with 90, and some non-rural got in with 95 (but I think they blitzed the UMAT and interview).
Oh yeh, and you need a bachelor degree with a credit average as a prerequisite to get into that postgrad med program -and you'll have to sit the GAMSAT, which I guess is like the UMAT all over again -I'd sure hate to do a 3 year degree then stuff up that test.