IMO it's too early for you to buy a MKSAP. First, considering what level of training you are, you would be better served using more basic review books than the MKSAP. It's actually probably too advanced for interns as well -- they would be better off using quick references like Up-To-Date given the limited time they have. Most people I know didn't even start looking at the MKSAP until the end of their last year of medicine residency.
The other consideration is that there is a new publication of the MKSAP every 2 years, and the books get outdated really fast. MKSAP 13 is the current publication, and many parts of it are already out of date. MKSAP 14 will be published in October, so if you're going to get it, you should at least wait for that. Keep in mind, though, that by the time you finish medicine residency and are studying for the Boards, your current edition will be MKSAP 15.
I don't think that this will help you for either step 3 or the wards -- the MKSAP contains way more detail than you'll ever need to know for step 3, so you would waste a lot of time studying the MKSAP at the expense of studying peds, ob/gyn, surgery, etc. Again, there are faster references that are more level-appropriate out there. The last consideration is that many programs have educational funds that they give to their residents - so you may be able to get your program to pay for it.
OK, I need to get back to studying my MKSAP now... 🙂
