I agree with UW and Secrets... I only got a 261 though, so take that for what it's worth =P
If you really like the StepUp series (I wasn't totally in love with SU to Med) I would think maybe SU to Step 2 would be better... since Medicine doesn't really go into Ob, Peds, etc. But if you already own the Medicine one, it would be pointless IMO to buy the other.